Encoder, decoder, encoding method, and decoding method

ABSTRACT

An encoder includes processing circuitry and a memory coupled to the processing circuitry. The processing circuitry is configured to: select a first filter for a first block based at least on a block size of the first block, the first filter including a first set of filter coefficients; select a second filter for a second block based at least on a block size of the second block, the second filter including a second set of filter coefficients; and change values of pixels in the first block and the second block to filter a boundary between the first block and the second block. The first set of filter coefficients applied in the first block and the second set of filter coefficients applied in the second block are selected to be asymmetrical with respect to the boundary based on the block size of the first block and the second block.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. continuation application of PCT InternationalPatent Application Number PCT/JP2018/014358 filed on Apr. 4, 2018,claiming the benefit of priority of U.S. Provisional Application No.62/482,359 filed on Apr. 6, 2017 and the benefit of priority of JapanesePatent Application Number 2017-106947 filed on May 30, 2017, the entirecontents of which are hereby incorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to encoders, decoders, encoding methods,and decoding methods.

2. Description of the Related Art

A video coding standard called high-efficiency video coding (HEVC) hasbeen standardized by Joint Collaborative Team on Video Coding (JCT-VC).

CITATION LIST Non-patent Literature

NPL 1: 11.265 (ISO/IEC 23008-2 HEVC)/HEVC (High Efficiency Video Coding)

SUMMARY

An encoder includes processing circuitry and a memory coupled to theprocessing circuitry. The processing circuitry is configured to: selecta first filter for a first block based at least on a block size of thefirst block, the first filter including a first set of filtercoefficients; select a second filter for a second block based at leaston a block size of the second block, the second filter including asecond set of filter coefficients; and change values of pixels in thefirst block and the second block to filter a boundary between the firstblock and the second block, by multiplying the values of pixels in thefirst block by the first set of filter coefficients, respectively, andmultiplying the values of pixels in the second block by the second setof filter coefficients, respectively, the pixels in the first block andthe second block being arranged along a line across the boundary. Thefirst set of filter coefficients applied in the first block and thesecond set of filter coefficients applied in the second block areselected to be asymmetrical with respect to the boundary based on theblock size of the first block and the second block.

It is to be noted that these general and specific aspects may beimplemented using a system, a method, an integrated circuit, a computerprogram, or a non-transitory computer-readable recording medium such asa CD-ROM, or any combination of systems, methods, integrated circuits,computer programs, or computer-readable recording media.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram illustrating a functional configuration of anencoder according to Embodiment 1.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1.

FIG. 3 is a chart indicating transform basis functions for eachtransform type.

FIG. 4A illustrates one example of a filter shape used in ALF.

FIG. 4B illustrates another example of a filter shape used in ALF.

FIG. 4C illustrates another example of a filter shape used in ALF.

FIG. 5A illustrates 67 intra prediction modes used in intra prediction.

FIG. 5B is a flow chart for illustrating an outline of a predictionimage correction process performed via OBMC processing.

FIG. 5C is a conceptual diagram for illustrating an outline of aprediction image correction process performed via OBMC processing.

FIG. 5D illustrates one example of FRUC.

FIG. 6 is for illustrating pattern matching (bilateral matching) betweentwo blocks along a motion trajectory.

FIG. 7 is for illustrating pattern matching (template matching) betweena template in the current picture and a block in a reference picture.

FIG. 8 is for illustrating a model assuming uniform linear motion.

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks.

FIG. 9B is for illustrating an outline of a process for deriving amotion vector via merge mode.

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing.

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing.

FIG. 10 is a block diagram illustrating a functional configuration of adecoder according to Embodiment 1.

FIG. 11 is a flowchart of deblocking filtering according to Embodiment1.

FIG. 12 is a diagram indicating an example of a pixel arrangement at aboundary according to Embodiment 1.

FIG. 13 is a flowchart of deblocking filtering according to Embodiment1.

FIG. 14 is a flowchart of deblocking filtering according to Embodiment2.

FIG. 15 is a diagram indicating relationships between pixel positionsand errors in blocks according to Embodiment 2.

FIG. 16 is a flowchart of deblocking filtering according to Embodiment3.

FIG. 17 is a diagram indicating DCT-II transform basis according toEmbodiment 3.

FIG. 18 is a diagram indicating DST-VII transform basis according toEmbodiment 3.

FIG. 19 is a flowchart of deblocking filtering according to Embodiment4.

FIG. 20 is a flowchart of deblocking filtering according to Embodiment5.

FIG. 21 is a diagram indicating examples of weights based on intraprediction directions and block boundary directions according toEmbodiment 5.

FIG. 22 is a flowchart of deblocking filtering according to Embodiment6.

FIG. 23 is a diagram indicating examples of weights based onquantization parameters according to Embodiment 6.

FIG. 24 illustrates an overall configuration of a content providingsystem for implementing a content distribution service.

FIG. 25 illustrates one example of an encoding structure in scalableencoding

FIG. 26 illustrates one example of an encoding structure in scalableencoding.

FIG. 27 illustrates an example of a display screen of a web page.

FIG. 28 illustrates an example of a display screen of a web page.

FIG. 29 illustrates one example of a smartphone.

FIG. 30 is a block diagram illustrating a configuration example of asmartphone.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the deblocking filtering in H.265/HEVC which is one of image codingmethods, a filter having a symmetrical characteristic across a blockboundary is applied. With this, when an error distribution isdiscontinuous as in an exemplary case where a pixel located at one sideacross a block boundary has a small error and a pixel located at theother side across the block boundary has a large error, performingsymmetrical filtering of the pixels may decrease an error reductionefficiency. Here, the error is a difference in pixel value between anoriginal image and a reconstructed image.

An encoder according to an aspect of the present disclosure includes: aprocessor; and memory, wherein, using the memory, the processor:determines a filter characteristic which is asymmetrical across a blockboundary; and performs deblocking filtering using the filtercharacteristic determined.

In this way, there is a possibility that the encoder can reduce theerror by performing filtering using the asymmetrical filtercharacteristic across the block boundary.

For example, when determining the filter characteristic, the processormay determine the asymmetrical filter characteristic so that a pixelwhich is more likely to have a large error with respect to an originalimage is more affected by the deblocking filtering.

In this way, there is a possibility that the encoder can further reducethe error in pixel value because the encoder is capable of increasingthe influence of the filtering on the pixel having the large error. Inaddition, there is a possibility that the encoder can reduce increase inthe error in pixel value because the encoder is capable of decreasingthe influence of the filtering on the pixel having the small error.

For example, when determining the filter characteristic, the processormay determine the asymmetrical filter characteristic by modifying filtercoefficients of a reference filter to be asymmetrical across the blockboundary.

For example, when determining the filter characteristic, the processormay determine asymmetrical weights across the block boundary, and in thedeblocking filtering, the processor may perform: a filter calculationusing filter coefficients; and weighting an amount of change in pixelvalue before and after the filter calculation using the asymmetricalweights determined.

For example, when determining the filter characteristic, the processormay determine asymmetrical offset values across the block boundary, andin the deblocking filtering, the processor may perform: a filtercalculation using filter coefficients; and an addition of theasymmetrical offset values determined to pixel values after the filtercalculation.

For example, when determining the filter characteristic, the processormay determine reference values which are asymmetrical across the blockboundary, in the deblocking filtering, the processor may perform: afilter calculation using filter coefficients; and when an amount ofchange in pixel value before and after the filter calculation exceeds acorresponding one of the reference values, clipping of the amount ofchange to the reference value.

For example, when determining the filter characteristic, the processormay set conditions for determining whether the deblocking filtering isto be performed, the conditions being asymmetrical across the blockboundary.

A decoder according to an aspect of the present disclosure includes: aprocessor; and memory, wherein, using the memory, the processor:determines a filter characteristic which is asymmetrical across a blockboundary; and performs deblocking filtering using the filtercharacteristic determined.

In this way, there is a possibility that the decoder can reduce theerror by performing filtering using the asymmetrical filtercharacteristic across the block boundary.

For example, when determining the filter characteristic, the processormay determine the asymmetrical filter characteristic so that a pixelwhich is more likely to have a large error with respect to an originalimage is more affected by the deblocking filtering.

In this way, there is a possibility that the decoder can further reducethe error in pixel value because the decoder is capable of increasingthe influence of the filtering on the pixel having the large error. Inaddition, there is a possibility that the decoder can reduce increase inthe error in pixel value because the decoder is capable of decreasingthe influence of the filtering on the pixel having the small error.

For example, when determining the filter characteristic, the processormay determine the asymmetrical filter characteristic by modifying filtercoefficients of a reference filter to be asymmetrical across the blockboundary.

For example, when determining the filter characteristic, the processormay determine asymmetrical weights across the block boundary, and in thedeblocking filtering, the processor may perform: a filter calculationusing filter coefficients; and weighting an amount of change in pixelvalue before and after the filter calculation using the asymmetricalweights determined.

For example, when determining the filter characteristic, the processormay determine asymmetrical offset values across the block boundary, andin the deblocking filtering, the processor may perform: a filtercalculation using filter coefficients; and an addition of theasymmetrical offset values determined to pixel values after the filtercalculation.

For example, when determining the filter characteristic, the processormay determine reference values which are asymmetrical across the blockboundary, in the deblocking filtering, the processor may perform: afilter calculation using filter coefficients; and when an amount ofchange in pixel value before and after the filter calculation exceeds acorresponding one of the reference values, clipping of the amount ofchange to the reference value.

For example, when determining the filter characteristic, the processormay set conditions for determining whether the deblocking filtering isto be performed, the conditions being asymmetrical across the blockboundary.

An encoding method according to an aspect of the present disclosureincludes: determining a filter characteristic which is asymmetricalacross a block boundary; and performing deblocking filtering using thefilter characteristic determined.

In this way, there is a possibility that the error can be reduced byperforming the encoding method involving filtering using theasymmetrical filter characteristic across the block boundary.

A decoding method according to an aspect of the present disclosureincludes: determining a filter characteristic which is asymmetricalacross a block boundary; and performing deblocking filtering using thefilter characteristic determined.

In this way, there is a possibility that the error can be reduced byperforming the decoding method involving filtering using theasymmetrical filter characteristic across the block boundary.

An encoder according to an aspect of the present disclosure includes: aprocessor; and memory, wherein, using the memory, the processor:determines a filter characteristic which is asymmetrical across a blockboundary, based on pixel values across the block boundary; and performsdeblocking filtering using the filter characteristic determined.

In this way, there is a possibility that the encoder can reduce theerror by performing filtering using the asymmetrical filtercharacteristic across the block boundary. In addition, the encoder iscapable of determining an appropriate filter characteristic based on thepixel values across the block boundary.

For example, when determining the filter characteristic, the processormay determine the filter characteristic based on a difference betweenthe pixel values.

For example, when determining the filter characteristic, the processormay increase a difference in the filter characteristic across the blockboundary with increase in difference in pixel value.

In this way, there is a possibility that the encoder can preventunnecessary smoothing from being performed when, for example, a blockboundary coincides with the edge of an object in an image.

For example, when determining the filter characteristic, the processor:may compare the difference between the pixel values with a thresholdvalue based on a quantization parameter; and increase the difference inthe filter characteristic across the boundary more significantly whenthe difference between the pixel values is larger than the thresholdvalue than when the difference between the pixel values is smaller thanthe threshold value.

In this way, the encoder is capable of determining the filtercharacteristic with consideration of the influence on the error inquantization parameter.

For example, when determining the filter characteristic, the processor:may decrease a difference in the filter characteristic across the blockboundary with increase in difference in pixel value.

In this way, there is a possibility that the decoder can reduce decreasein smoothing effect by the asymmetry when a block boundary issubjectively noticeable, thereby reducing the decrease in subjectiveimage quality.

For example, when determining the filter characteristic, the processor:may determine the filter characteristic based on a variance of the pixelvalues.

A decoder according to an aspect of the present disclosure includes: aprocessor; and memory, wherein, using the memory, the processor:determines a filter characteristic which is asymmetrical across a blockboundary, based on pixel values across the block boundary; and performsdeblocking filtering using the filter characteristic determined.

In this way, there is a possibility that the decoder can reduce theerror by performing filtering using the asymmetrical filtercharacteristic across the block boundary. In addition, there is apossibility that the decoder can determine an appropriate filtercharacteristic based on the pixel values across the block boundary.

For example, when determining the filter characteristic, the processormay determine the filter characteristic based on a difference betweenthe pixel values.

For example, when determining the filter characteristic, the processormay increase a difference in the filter characteristic across the blockboundary with increase in difference in pixel value.

In this way, there is a possibility that the decoder can further reducethe error in pixel value because the decoder is capable of increasingthe influence of the filtering on the pixel having the large error. Inaddition, there is a possibility that the decoder can reduce increase inthe error in pixel value because the decoder is capable of decreasingthe influence of the filtering on the pixel having the small error.

For example, when determining the filter characteristic, the processor:may compare the difference between the pixel values with a thresholdvalue based on a quantization parameter; and increase the difference inthe filter characteristic across the boundary more significantly whenthe difference between the pixel values is larger than the thresholdvalue than when the difference between the pixel values is smaller thanthe threshold value.

In this way, the decoder is capable of determining the filtercharacteristic with consideration of the influence on the error inquantization parameter.

For example, when determining the filter characteristic, the processor:may decrease a difference in the filter characteristic across the blockboundary with increase in difference in pixel value.

In this way, there is a possibility that the decoder can preventunnecessary smoothing from being performed when, for example, a blockboundary coincides with the edge of an object in an image.

For example, when determining the filter characteristic, the processor:may determine the filter characteristic based on a variance of the pixelvalues.

An encoding method according to an aspect of the present disclosureincludes: determining a filter characteristic which is asymmetricalacross a block boundary, based on pixel values across the blockboundary; and performing deblocking filtering using the filtercharacteristic determined.

In this way, there is a possibility that the error can be reduced byperforming the encoding method involving filtering using theasymmetrical filter characteristic across the block boundary. Inaddition, the encoding method makes it possible to determine anappropriate filter characteristic based on the difference between thepixel values across the block boundary.

A decoding method according to an aspect of the present disclosureincludes: determining a filter characteristic which is asymmetricalacross a block boundary, based on pixel values across the blockboundary; and performing deblocking filtering using the filtercharacteristic determined.

In this way, there is a possibility that the error can be reduced byperforming the decoding method involving filtering using theasymmetrical filter characteristic across the block boundary. Inaddition, the decoding method makes it possible to determine anappropriate filter characteristic based on the difference between thepixel values across the block boundary.

An encoder according to an aspect of the present disclosure includes: aprocessor; and memory, wherein, using the memory, the processor:determines a filter characteristic which is asymmetrical across a blockboundary, based on an angle between the block boundary and a predictiondirection in intra prediction; and performs deblocking filtering usingthe filter characteristic determined.

In this way, there is a possibility that the encoder can reduce theerror by performing filtering using the asymmetrical filtercharacteristic across the block boundary. In addition, the encoder iscapable of determining an appropriate filter characteristic based on theangle between the block boundary and the prediction direction in intraprediction.

For example, when determining the filter characteristic, the processormay increase a difference in the filter characteristic across the blockboundary when the angle is closer to a vertical axis.

In this way, there is a possibility that the encoder can further reducethe error in pixel value because the encoder is capable of increasingthe influence of the filtering on the pixel having the large error. Inaddition, there is a possibility that the encoder can reduce increase inthe error in pixel value because the encoder is capable of decreasingthe influence of the filtering on the pixel having the small error.

For example, when determining the filter characteristic, the processormay decrease a difference in the filter characteristic across the blockboundary when the angle is closer to a horizontal axis.

In this way, there is a possibility that the encoder can further reducethe error in pixel value because the encoder is capable of increasingthe influence of the filtering on the pixel having the large error. Inaddition, there is a possibility that the encoder can reduce increase inthe error in pixel value because the encoder is capable of decreasingthe influence of the filtering on the pixel having the small error.

A decoder according to an aspect of the present disclosure includes: aprocessor; and memory, wherein, using the memory, the processor:determines a filter characteristic which is asymmetrical across a blockboundary, based on an angle between the block boundary and a predictiondirection in intra prediction;

and performs deblocking filtering using the filter characteristicdetermined.

In this way, there is a possibility that the decoder can reduce theerror by performing filtering using the asymmetrical filtercharacteristic across the block boundary. In addition, there is apossibility that the decoder can determine an appropriate filtercharacteristic based on the angle between the block boundary and theprediction direction in intra prediction.

For example, when determining the filter characteristic, the processormay increase a difference in the filter characteristic across the blockboundary when the angle is closer to a vertical axis.

In this way, there is a possibility that the decoder can further reducethe error in pixel value because the decoder is capable of increasingthe influence of the filtering on the pixel having the large error. Inaddition, there is a possibility that the decoder can reduce increase inthe error in pixel value because the decoder is capable of decreasingthe influence of the filtering on the pixel having the small error.

For example, when determining the filter characteristic, the processormay decrease a difference in the filter characteristic across the blockboundary when the angle is closer to a horizontal axis.

In this way, there is a possibility that the decoder can further reducethe error in pixel value because the decoder is capable of increasingthe influence of the filtering on the pixel having the large error. Inaddition, there is a possibility that the decoder can reduce increase inthe error in pixel value because the decoder is capable of decreasingthe influence of the filtering on the pixel having the small error.

An encoding method according to an aspect of the present disclosureincludes: determining a filter characteristic which is asymmetricalacross a block boundary, based on an angle between the block boundaryand a prediction direction in intra prediction; and performingdeblocking filtering using the filter characteristic determined.

In this way, there is a possibility that the error can be reduced byperforming the encoding method involving filtering using theasymmetrical filter characteristic across the block boundary. Inaddition, the encoding method makes it possible to determine anappropriate filter characteristic based on the angle between the blockboundary and the prediction direction in intra prediction.

A decoding method according to an aspect of the present disclosureincludes: determining a filter characteristic which is asymmetricalacross a block boundary, based on an angle between the block boundaryand a prediction direction in intra prediction; and performingdeblocking filtering using the filter characteristic determined.

In this way, there is a possibility that the error can be reduced byperforming the decoding method involving filtering using theasymmetrical filter characteristic across the block boundary. Inaddition, the decoding method makes it possible to determine anappropriate filter characteristic based on the angle between the blockboundary and the prediction direction in intra prediction.

An encoder according to an aspect of the present disclosure includes: aprocessor; and memory, wherein, using the memory, the processor:determines a filter characteristic which is asymmetrical across a blockboundary, based on a position of a current pixel in a block; andperforms, on the current pixel, deblocking filtering using the filtercharacteristic determined.

In this way, there is a possibility that the encoder can reduce theerror by performing filtering using the asymmetrical filtercharacteristic across the block boundary. In addition, the encoder iscapable of determining an appropriate filter characteristic based on theposition of the current pixel in the block.

For example, when determining the filter characteristic, the processormay determine the filter characteristic so that a pixel which is moredistant from a reference pixel for intra prediction is more affected bythe deblocking filtering.

In this way, there is a possibility that the encoder can further reducethe error in pixel value because the encoder is capable of increasingthe influence of the filtering on the pixel having the large error. Inaddition, there is a possibility that the encoder can reduce increase inthe error in pixel value because the encoder is capable of decreasingthe influence of the filtering on the pixel having the small error.

For example, when determining the filter characteristic, the processormay determine the filter characteristic so that a lower-right pixel ismore affected by the deblocking filtering than an upper-left pixel.

In this way, there is a possibility that the encoder can further reducethe error in pixel value because the encoder is capable of increasingthe influence of the filtering on the pixel having the large error. Inaddition, there is a possibility that the encoder can reduce increase inthe error in pixel value because the encoder is capable of decreasingthe influence of the filtering on the pixel having the small error.

A decoder according to an aspect of the present disclosure includes: aprocessor; and memory, wherein, using the memory, the processor:determines a filter characteristic which is asymmetrical across a blockboundary, based on a position of a current pixel in a block; andperforms, on the current pixel, deblocking filtering using the filtercharacteristic determined.

In this way, there is a possibility that the decoder can reduce theerror by performing filtering using the asymmetrical filtercharacteristic across the block boundary. In addition, the decoder iscapable of determining an appropriate filter characteristic based on theposition of the current pixel in the block.

For example, when determining the filter characteristic, the processormay determine the filter characteristic so that a pixel which is moredistant from a reference pixel for intra prediction is more affected bythe deblocking filtering.

In this way, there is a possibility that the decoder can further reducethe error in pixel value because the decoder is capable of increasingthe influence of the filtering on the pixel having the large error. Inaddition, there is a possibility that the decoder can reduce increase inthe error in pixel value because the decoder is capable of decreasingthe influence of the filtering on the pixel having the small error.

For example, when determining the filter characteristic, the processormay determine the filter characteristic so that a lower-right pixel ismore affected by the deblocking filtering than an upper-left pixel.

In this way, there is a possibility that the decoder can further reducethe error in pixel value because the decoder is capable of increasingthe influence of the filtering on the pixel having the large error. Inaddition, there is a possibility that the decoder can reduce increase inthe error in pixel value because the decoder is capable of decreasingthe influence of the filtering on the pixel having the small error.

An encoding method according to an aspect of the present disclosureincludes: determining a filter characteristic which is asymmetricalacross a block boundary, based on a position of a current pixel in ablock; and performing deblocking filtering using the filtercharacteristic determined.

In this way, there is a possibility that the error can be reduced byperforming the encoding method involving filtering using theasymmetrical filter characteristic across the block boundary. Inaddition, the encoding method makes it possible to determine anappropriate filter characteristic based on the position of the currentpixel in the block.

A decoding method according to an aspect of the present disclosureincludes: determining a filter characteristic which is asymmetricalacross a block boundary, based on a position of a current pixel in ablock; and performing deblocking filtering using the filtercharacteristic determined.

In this way, there is a possibility that the error can be reduced byperforming the decoding method involving filtering using theasymmetrical filter characteristic across the block boundary. Inaddition, the decoding method makes it possible to determine anappropriate filter characteristic based on the position of the currentpixel in the block.

An encoder according to an aspect of the present disclosure includes: aprocessor; and memory, wherein, using the memory, the processor:determines a filter characteristic which is asymmetrical across a blockboundary, based on a quantization parameter; and performs deblockingfiltering using the filter characteristic determined.

In this way, there is a possibility that the encoder can reduce theerror by performing filtering using the asymmetrical filtercharacteristic across the block boundary. Furthermore, the encoder iscapable of determining an appropriate filter characteristic based on aquantization parameter.

For example, when determining the filter characteristic, the processormay determine the filter characteristic so that influence of thedeblocking filtering becomes larger as a quantization parameter becomeslarger.

In this way, there is a possibility that the encoder can further reducethe error in pixel value because the encoder is capable of increasingthe influence of the filtering on the pixel having the large error. Inaddition, there is a possibility that the encoder can reduce increase inthe error in pixel value because the encoder is capable of decreasingthe influence of the filtering on the pixel having the small error.

For example, when determining the filter characteristic, the processormay determine the filter characteristic so that change in influence offiltering with changing quantization parameter for an upper-left pixelbecomes larger than change in influence of filtering with changingquantization parameter for a lower-right pixel.

In this way, there is a possibility that the encoder can further reducethe error in pixel value because the encoder is capable of increasingthe influence of the filtering on the pixel having the large error.

A decoder according to an aspect of the present disclosure includes: aprocessor; and memory, wherein, using the memory, the processor:determines a filter characteristic which is asymmetrical across a blockboundary, based on a quantization parameter; and performs deblockingfiltering using the filter characteristic determined.

In this way, there is a possibility that the decoder can reduce theerror by performing filtering using the asymmetrical filtercharacteristic across the block boundary. Furthermore, the decoder iscapable of determining an appropriate filter characteristic based on aquantization parameter.

For example, when determining the filter characteristic, the processormay determine the filter characteristic so that influence of thedeblocking filtering becomes larger as a quantization parameter becomeslarger.

In this way, there is a possibility that the decoder can further reducethe error in pixel value because the decoder is capable of increasingthe influence of the filtering on the pixel having the large error. Inaddition, there is a possibility that the decoder can reduce increase inthe error in pixel value because the decoder is capable of decreasingthe influence of the filtering on the pixel having the small error.

For example, when determining the filter characteristic, the processormay determine the filter characteristic so that change in influence offiltering with changing quantization parameter for an upper-left pixelbecomes larger than change in influence of filtering with changingquantization parameter for a lower-right pixel.

In this way, there is a possibility that the decoder can further reducethe error in pixel value because the decoder is capable of increasingthe influence of the filtering on the pixel having the large error.

An encoding method according to an aspect of the present disclosure mayinclude: determining a filter characteristic which is asymmetricalacross a block boundary, based on a quantization parameter; andperforming deblocking filtering using the filter characteristicdetermined.

In this way, there is a possibility that the error can be reduced byperforming the encoding method involving filtering using theasymmetrical filter characteristic across the block boundary.Furthermore, the encoding method makes it possible to determine anappropriate filter characteristic based on a quantization parameter.

A decoding method according to an aspect of the present disclosure mayinclude: determining a filter characteristic which is asymmetricalacross a block boundary, based on a quantization parameter; andperforming deblocking filtering using the filter characteristicdetermined.

In this way, there is a possibility that the error can be reduced byperforming the decoding method involving filtering using theasymmetrical filter characteristic across the block boundary.Furthermore, the decoding method makes it possible to determine anappropriate filter characteristic based on a quantization parameter.

It is to be noted that these general and specific aspects may beimplemented using a system, a method, an integrated circuit, a computerprogram, or a non-transitory computer-readable recording medium such asa CD-ROM, or any combination of systems, methods, integrated circuits,computer programs, or computer-readable recording media.

Hereinafter, embodiments are described in detail with reference to thedrawings.

It is to be noted that the embodiments described below each show ageneral or specific example. The numerical values, shapes, materials,constituent elements, the arrangement and connection of the constituentelements, steps, order of the steps, etc., indicated in the followingembodiments are mere examples, and therefore are not intended to limitthe scope of the claims. Therefore, among the constituent elements inthe following embodiments, those not recited in any of the independentclaims defining the most generic inventive concepts are described asoptional constituent elements.

Embodiment 1

First, an outline of Embodiment 1 will be presented. Embodiment 1 is oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in subsequent description of aspects of thepresent disclosure are applicable. Note that Embodiment 1 is merely oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in the description of aspects of the presentdisclosure are applicable. The processes and/or configurations presentedin the description of aspects of the present disclosure can also beimplemented in an encoder and a decoder different from those accordingto Embodiment 1.

When the processes and/or configurations presented in the description ofaspects of the present disclosure are applied to Embodiment 1, forexample, any of the following may be performed.

(1) regarding the encoder or the decoder according to Embodiment 1,among components included in the encoder or the decoder according toEmbodiment 1, substituting a component corresponding to a componentpresented in the description of aspects of the present disclosure with acomponent presented in the description of aspects of the presentdisclosure;

(2) regarding the encoder or the decoder according to Embodiment 1,implementing discretionary changes to functions or implemented processesperformed by one or more components included in the encoder or thedecoder according to Embodiment 1, such as addition, substitution, orremoval, etc., of such functions or implemented processes, thensubstituting a component corresponding to a component presented in thedescription of aspects of the present disclosure with a componentpresented in the description of aspects of the present disclosure;

(3) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, implementing discretionary changes such asaddition of processes and/or substitution, removal of one or more of theprocesses included in the method, and then substituting a processescorresponding to a process presented in the description of aspects ofthe present disclosure with a process presented in the description ofaspects of the present disclosure;

(4) combining one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(5) combining a component including one or more functions included inone or more components included in the encoder or the decoder accordingto Embodiment 1, or a component that implements one or more processesimplemented by one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(6) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, among processes included in the method,substituting a process corresponding to a process presented in thedescription of aspects of the present disclosure with a processpresented in the description of aspects of the present disclosure; and

(7) combining one or more processes included in the method implementedby the encoder or the decoder according to Embodiment 1 with a processpresented in the description of aspects of the present disclosure.

Note that the implementation of the processes and/or configurationspresented in the description of aspects of the present disclosure is notlimited to the above examples. For example, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be implemented in a device used for a purpose differentfrom the moving picture/picture encoder or the moving picture/picturedecoder disclosed in Embodiment 1. Moreover, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be independently implemented. Moreover, processes and/orconfigurations described in different aspects may be combined.

[Encoder Outline]

First, the encoder according to Embodiment 1 will be outlined. FIG. 1 isa block diagram illustrating a functional configuration of encoder 100according to Embodiment 1. Encoder 100 is a moving picture/pictureencoder that encodes a moving picture/picture block by block.

As illustrated in FIG. 1, encoder 100 is a device that encodes a pictureblock by block, and includes splitter 102, subtractor 104, transformer106, quantizer 108, entropy encoder 110, inverse quantizer 112, inversetransformer 114, adder 116, block memory 118, loop filter 120, framememory 122, intra predictor 124, inter predictor 126, and predictioncontroller 128.

Encoder 100 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as splitter 102, subtractor104, transformer 106, quantizer 108, entropy encoder 110, inversequantizer 112, inverse transformer 114, adder 116, loop filter 120,intra predictor 124, inter predictor 126, and prediction controller 128.Alternatively, encoder 100 may be realized as one or more dedicatedelectronic circuits corresponding to splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, loop filter 120, intrapredictor 124, inter predictor 126, and prediction controller 128.

Hereinafter, each component included in encoder 100 will be described.

[Splitter]

Splitter 102 splits each picture included in an input moving pictureinto blocks, and outputs each block to subtractor 104. For example,splitter 102 first splits a picture into blocks of a fixed size (forexample, 128×128). The fixed size block is also referred to as codingtree unit (CTU). Splitter 102 then splits each fixed size block intoblocks of variable sizes (for example, 64×64 or smaller), based onrecursive quadtree and/or binary tree block splitting. The variable sizeblock is also referred to as a coding unit (CU), a prediction unit (PU),or a transform unit (TU). Note that in this embodiment, there is no needto differentiate between CU, PU, and TU; all or some of the blocks in apicture may be processed per CU, PU, or TU.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1. In FIG. 2, the solid lines represent block boundaries ofblocks split by quadtree block splitting, and the dashed lines representblock boundaries of blocks split by binary tree block splitting.

Here, block 10 is a square 128×128 pixel block (128×128 block). This128×128 block 10 is first split into four square 64×64 blocks (quadtreeblock splitting).

The top left 64×64 block is further vertically split into two rectangle32×64 blocks, and the left 32×64 block is further vertically split intotwo rectangle 16×64 blocks (binary tree block splitting). As a result,the top left 64×64 block is split into two 16×64 blocks 11 and 12 andone 32×64 block 13.

The top right 64×64 block is horizontally split into two rectangle 64×32blocks 14 and 15 (binary tree block splitting).

The bottom left 64×64 block is first split into four square 32×32 blocks(quadtree block splitting). The top left block and the bottom rightblock among the four 32×32 blocks are further split. The top left 32×32block is vertically split into two rectangle 16×32 blocks, and the right16×32 block is further horizontally split into two 16×16 blocks (binarytree block splitting). The bottom right 32×32 block is horizontallysplit into two 32×16 blocks (binary tree block splitting). As a result,the bottom left 64×64 block is split into 16×32 block 16, two 16×16blocks 17 and 18, two 32×32 blocks 19 and 20, and two 32×16 blocks 21and 22.

The bottom right 64×64 block 23 is not split.

As described above, in FIG. 2, block 10 is split into 13 variable sizeblocks 11 through 23 based on recursive quadtree and binary tree blocksplitting. This type of splitting is also referred to as quadtree plusbinary tree (QTBT) splitting.

Note that in FIG. 2, one block is split into four or two blocks(quadtree or binary tree block splitting), but splitting is not limitedto this example. For example, one block may be split into three blocks(ternary block splitting).

Splitting including such ternary block splitting is also referred to asmulti-type tree (MBT) splitting.

[Subtractor]

Subtractor 104 subtracts a prediction signal (prediction sample) from anoriginal signal (original sample) per block split by splitter 102. Inother words, subtractor 104 calculates prediction errors (also referredto as residuals) of a block to be encoded (hereinafter referred to as acurrent block). Subtractor 104 then outputs the calculated predictionerrors to transformer 106.

The original signal is a signal input into encoder 100, and is a signalrepresenting an image for each picture included in a moving picture (forexample, a luma signal and two chroma signals). Hereinafter, a signalrepresenting an image is also referred to as a sample.

[Transformer]

Transformer 106 transforms spatial domain prediction errors intofrequency domain transform coefficients, and outputs the transformcoefficients to quantizer 108. More specifically, transformer 106applies, for example, a predefined discrete cosine transform (DCT) ordiscrete sine transform (DST) to spatial domain prediction errors.

Note that transformer 106 may adaptively select a transform type fromamong a plurality of transform types, and transform prediction errorsinto transform coefficients by using a transform basis functioncorresponding to the selected transform type. This sort of transform isalso referred to as explicit multiple core transform (EMT) or adaptivemultiple transform (AMT).

The transform types include, for example, DCT-II, DCT-V, DCT-VIII,DST-I, and DST-VII. FIG. 3 is a chart indicating transform basisfunctions for each transform type. In FIG. 3, N indicates the number ofinput pixels. For example, selection of a transform type from among theplurality of transform types may depend on the prediction type (intraprediction and inter prediction), and may depend on intra predictionmode.

Information indicating whether to apply such EMT or AMT (referred to as,for example, an AMT flag) and information indicating the selectedtransform type is signalled at the CU level. Note that the signaling ofsuch information need not be performed at the CU level, and may beperformed at another level (for example, at the sequence level, picturelevel, slice level, tile level, or CTU level).

Moreover, transformer 106 may apply a secondary transform to thetransform coefficients (transform result). Such a secondary transform isalso referred to as adaptive secondary transform (AST) or non-separablesecondary transform (NSST). For example, transformer 106 applies asecondary transform to each sub-block (for example, each 4×4 sub-block)included in the block of the transform coefficients corresponding to theintra prediction errors. Information indicating whether to apply NSSTand information related to the transform matrix used in NSST aresignalled at the CU level. Note that the signaling of such informationneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, or CTU level).

Here, a separable transform is a method in which a transform isperformed a plurality of times by separately performing a transform foreach direction according to the number of dimensions input. Anon-separable transform is a method of performing a collective transformin which two or more dimensions in a multidimensional input arecollectively regarded as a single dimension.

In one example of a non-separable transform, when the input is a 4×4block, the 4×4 block is regarded as a single array including 16components, and the transform applies a 16×16 transform matrix to thearray.

Moreover, similar to above, after an input 4×4 block is regarded as asingle array including 16 components, a transform that performs aplurality of Givens rotations on the array (i.e., a Hypercube-GivensTransform) is also one example of a non-separable transform.

[Quantizer]

Quantizer 108 quantizes the transform coefficients output fromtransformer 106. More specifically, quantizer 108 scans, in apredetermined scanning order, the transform coefficients of the currentblock, and quantizes the scanned transform coefficients based onquantization parameters (QP) corresponding to the transformcoefficients. Quantizer 108 then outputs the quantized transformcoefficients (hereinafter referred to as quantized coefficients) of thecurrent block to entropy encoder 110 and inverse quantizer 112.

A predetermined order is an order for quantizing/inverse quantizingtransform coefficients. For example, a predetermined scanning order isdefined as ascending order of frequency (from low to high frequency) ordescending order of frequency (from high to low frequency).

A quantization parameter is a parameter defining a quantization stepsize (quantization width). For example, if the value of the quantizationparameter increases, the quantization step size also increases. In otherwords, if the value of the quantization parameter increases, thequantization error increases.

[Entropy Encoder]

Entropy encoder 110 generates an encoded signal (encoded bitstream) byvariable length encoding quantized coefficients, which are inputs fromquantizer 108. More specifically, entropy encoder 110, for example,binarizes quantized coefficients and arithmetic encodes the binarysignal.

[Inverse Quantizer]

Inverse quantizer 112 inverse quantizes quantized coefficients, whichare inputs from quantizer 108. More specifically, inverse quantizer 112inverse quantizes, in a predetermined scanning order, quantizedcoefficients of the current block. Inverse quantizer 112 then outputsthe inverse quantized transform coefficients of the current block toinverse transformer 114.

[Inverse Transformer]

Inverse transformer 114 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 112. More specifically, inverse transformer 114 restores theprediction errors of the current block by applying an inverse transformcorresponding to the transform applied by transformer 106 on thetransform coefficients. Inverse transformer 114 then outputs therestored prediction errors to adder 116.

Note that since information is lost in quantization, the restoredprediction errors do not match the prediction errors calculated bysubtractor 104. In other words, the restored prediction errors includequantization errors.

[Adder]

Adder 116 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 114, and prediction samples,which are inputs from prediction controller 128. Adder 116 then outputsthe reconstructed block to block memory 118 and loop filter 120. Areconstructed block is also referred to as a local decoded block.

[Block Memory]

Block memory 118 is storage for storing blocks in a picture to beencoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 118 storesreconstructed blocks output from adder 116.

[Loop Filter]

Loop filter 120 applies a loop filter to blocks reconstructed by adder116, and outputs the filtered reconstructed blocks to frame memory 122.A loop filter is a filter used in an encoding loop (in-loop filter), andincludes, for example, a deblocking filter (DF), a sample adaptiveoffset (SAO), and an adaptive loop filter (ALF).

In ALF, a least square error filter for removing compression artifactsis applied. For example, one filter from among a plurality of filters isselected for each 2×2 sub-block in the current block based on directionand activity of local gradients, and is applied.

More specifically, first, each sub-block (for example, each 2×2sub-block) is categorized into one out of a plurality of classes (forexample, 15 or 25 classes). The classification of the sub-block is basedon gradient directionality and activity. For example, classificationindex C is derived based on gradient directionality D (for example, 0 to2 or 0 to 4) and gradient activity A (for example, 0 to 4) (for example,C=5D+A). Then, based on classification index C, each sub-block iscategorized into one out of a plurality of classes (for example, 15 or25 classes).

For example, gradient directionality D is calculated by comparinggradients of a plurality of directions (for example, the horizontal,vertical, and two diagonal directions). Moreover, for example, gradientactivity A is calculated by summing gradients of a plurality ofdirections and quantizing the sum.

The filter to be used for each sub-block is determined from among theplurality of filters based on the result of such categorization.

The filter shape to be used in ALF is, for example, a circular symmetricfilter shape. FIG. 4A through FIG. 4C illustrate examples of filtershapes used in ALF. FIG. 4A illustrates a 5×5 diamond shape filter, FIG.4B illustrates a 7×7 diamond shape filter, and FIG. 4C illustrates a 9×9diamond shape filter. Information indicating the filter shape issignalled at the picture level. Note that the signaling of informationindicating the filter shape need not be performed at the picture level,and may be performed at another level (for example, at the sequencelevel, slice level, tile level, CTU level, or CU level).

The enabling or disabling of ALF is determined at the picture level orCU level. For example, for luma, the decision to apply ALF or not isdone at the CU level, and for chroma, the decision to apply ALF or notis done at the picture level. Information indicating whether ALF isenabled or disabled is signalled at the picture level or CU level. Notethat the signaling of information indicating whether ALF is enabled ordisabled need not be performed at the picture level or CU level, and maybe performed at another level (for example, at the sequence level, slicelevel, tile level, or CTU level).

The coefficients set for the plurality of selectable filters (forexample, 15 or 25 filters) are signalled at the picture level. Note thatthe signaling of the coefficients set need not be performed at thepicture level, and may be performed at another level (for example, atthe sequence level, slice level, tile level, CTU level, CU level, orsub-block level).

[Frame Memory]

Frame memory 122 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 122 stores reconstructed blocks filtered byloop filter 120.

[Intra Predictor]

Intra predictor 124 generates a prediction signal (intra predictionsignal) by intra predicting the current block with reference to a blockor blocks in the current picture and stored in block memory 118 (alsoreferred to as intra frame prediction). More specifically, intrapredictor 124 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 128.

For example, intra predictor 124 performs intra prediction by using onemode from among a plurality of predefined intra prediction modes. Theintra prediction modes include one or more non-directional predictionmodes and a plurality of directional prediction modes.

The one or more non-directional prediction modes include, for example,planar prediction mode and DC prediction mode defined in theH.265/high-efficiency video coding (HEVC) standard (see NPTL 1).

The plurality of directional prediction modes include, for example, the33 directional prediction modes defined in the H.265/HEVC standard. Notethat the plurality of directional prediction modes may further include32 directional prediction modes in addition to the 33 directionalprediction modes (for a total of 65 directional prediction modes). FIG.5A illustrates 67 intra prediction modes used in intra prediction (twonon-directional prediction modes and 65 directional prediction modes).The solid arrows represent the 33 directions defined in the H.265/HEVCstandard, and the dashed arrows represent the additional 32 directions.

Note that a luma block may be referenced in chroma block intraprediction. In other words, a chroma component of the current block maybe predicted based on a luma component of the current block. Such intraprediction is also referred to as cross-component linear model (CCLM)prediction. Such a chroma block intra prediction mode that references aluma block (referred to as, for example, CCLM mode) may be added as oneof the chroma block intra prediction modes.

Intra predictor 124 may correct post-intra-prediction pixel values basedon horizontal/vertical reference pixel gradients. Intra predictionaccompanied by this sort of correcting is also referred to as positiondependent intra prediction combination (PDPC). Information indicatingwhether to apply PDPC or not (referred to as, for example, a PDPC flag)is, for example, signalled at the CU level. Note that the signaling ofthis information need not be performed at the CU level, and may beperformed at another level (for example, on the sequence level, picturelevel, slice level, tile level, or CTU level).

[Inter Predictor]

Inter predictor 126 generates a prediction signal (inter predictionsignal) by inter predicting the current block with reference to a blockor blocks in a reference picture, which is different from the currentpicture and is stored in frame memory 122 (also referred to as interframe prediction). Inter prediction is performed per current block orper sub-block (for example, per 4×4 block) in the current block. Forexample, inter predictor 126 performs motion estimation in a referencepicture for the current block or sub-block. Inter predictor 126 thengenerates an inter prediction signal of the current block or sub-blockby motion compensation by using motion information (for example, amotion vector) obtained from motion estimation. Inter predictor 126 thenoutputs the generated inter prediction signal to prediction controller128.

The motion information used in motion compensation is signalled. Amotion vector predictor may be used for the signaling of the motionvector. In other words, the difference between the motion vector and themotion vector predictor may be signalled.

Note that the inter prediction signal may be generated using motioninformation for a neighboring block in addition to motion informationfor the current block obtained from motion estimation. Morespecifically, the inter prediction signal may be generated per sub-blockin the current block by calculating a weighted sum of a predictionsignal based on motion information obtained from motion estimation and aprediction signal based on motion information for a neighboring block.Such inter prediction (motion compensation) is also referred to asoverlapped block motion compensation (OBMC).

In such an OBMC mode, information indicating sub-block size for OBMC(referred to as, for example, OBMC block size) is signalled at thesequence level. Moreover, information indicating whether to apply theOBMC mode or not (referred to as, for example, an OBMC flag) issignalled at the CU level. Note that the signaling of such informationneed not be performed at the sequence level and CU level, and may beperformed at another level (for example, at the picture level, slicelevel, tile level, CTU level, or sub-block level).

Hereinafter, the OBMC mode will be described in further detail. FIG. 5Bis a flowchart and FIG. 5C is a conceptual diagram for illustrating anoutline of a prediction image correction process performed via OBMCprocessing.

First, a prediction image (Pred) is obtained through typical motioncompensation using a motion vector (MV) assigned to the current block.

Next, a prediction image (Pred_L) is obtained by applying a motionvector (MV_L) of the encoded neighboring left block to the currentblock, and a first pass of the correction of the prediction image ismade by superimposing the prediction image and Pred_L.

Similarly, a prediction image (Pred_U) is obtained by applying a motionvector (MV_U) of the encoded neighboring upper block to the currentblock, and a second pass of the correction of the prediction image ismade by superimposing the prediction image resulting from the first passand Pred_U. The result of the second pass is the final prediction image.

Note that the above example is of a two-pass correction method using theneighboring left and upper blocks, but the method may be a three-pass orhigher correction method that also uses the neighboring right and/orlower block.

Note that the region subject to superimposition may be the entire pixelregion of the block, and, alternatively, may be a partial block boundaryregion.

Note that here, the prediction image correction process is described asbeing based on a single reference picture, but the same applies when aprediction image is corrected based on a plurality of referencepictures. In such a case, after corrected prediction images resultingfrom performing correction based on each of the reference pictures areobtained, the obtained corrected prediction images are furthersuperimposed to obtain the final prediction image.

Note that the unit of the current block may be a prediction block and,alternatively, may be a sub-block obtained by further dividing theprediction block.

One example of a method for determining whether to implement OBMCprocessing is by using an obmc_flag, which is a signal that indicateswhether to implement OBMC processing. As one specific example, theencoder determines whether the current block belongs to a regionincluding complicated motion. The encoder sets the obmc_flag to a valueof “1” when the block belongs to a region including complicated motionand implements OBMC processing when encoding, and sets the obmc_flag toa value of “0” when the block does not belong to a region includingcomplication motion and encodes without implementing OBMC processing.The decoder switches between implementing OBMC processing or not bydecoding the obmc_flag written in the stream and performing the decodingin accordance with the flag value.

Note that the motion information may be derived on the decoder sidewithout being signalled. For example, a merge mode defined in theH.265/HEVC standard may be used. Moreover, for example, the motioninformation may be derived by performing motion estimation on thedecoder side. In this case, motion estimation is performed without usingthe pixel values of the current block.

Here, a mode for performing motion estimation on the decoder side willbe described. A mode for performing motion estimation on the decoderside is also referred to as pattern matched motion vector derivation(PMMVD) mode or frame rate up-conversion (FRUC) mode.

One example of FRUC processing is illustrated in FIG. 5D. First, acandidate list (a candidate list may be a merge list) of candidates eachincluding a motion vector predictor is generated with reference tomotion vectors of encoded blocks that spatially or temporally neighborthe current block. Next, the best candidate MV is selected from among aplurality of candidate MVs registered in the candidate list. Forexample, evaluation values for the candidates included in the candidatelist are calculated and one candidate is selected based on thecalculated evaluation values.

Next, a motion vector for the current block is derived from the motionvector of the selected candidate. More specifically, for example, themotion vector for the current block is calculated as the motion vectorof the selected candidate (best candidate MV), as-is. Alternatively, themotion vector for the current block may be derived by pattern matchingperformed in the vicinity of a position in a reference picturecorresponding to the motion vector of the selected candidate. In otherwords, when the vicinity of the best candidate MV is searched via thesame method and an MV having a better evaluation value is found, thebest candidate MV may be updated to the MV having the better evaluationvalue, and the MV having the better evaluation value may be used as thefinal MV for the current block. Note that a configuration in which thisprocessing is not implemented is also acceptable.

The same processes may be performed in cases in which the processing isperformed in units of sub-blocks.

Note that an evaluation value is calculated by calculating thedifference in the reconstructed image by pattern matching performedbetween a region in a reference picture corresponding to a motion vectorand a predetermined region. Note that the evaluation value may becalculated by using some other information in addition to thedifference.

The pattern matching used is either first pattern matching or secondpattern matching. First pattern matching and second pattern matching arealso referred to as bilateral matching and template matching,respectively.

In the first pattern matching, pattern matching is performed between twoblocks along the motion trajectory of the current block in two differentreference pictures. Therefore, in the first pattern matching, a regionin another reference picture conforming to the motion trajectory of thecurrent block is used as the predetermined region for theabove-described calculation of the candidate evaluation value.

FIG. 6 is for illustrating one example of pattern matching (bilateralmatching) between two blocks along a motion trajectory. As illustratedin FIG. 6, in the first pattern matching, two motion vectors (MV0, MV1)are derived by finding the best match between two blocks along themotion trajectory of the current block (Cur block) in two differentreference pictures (Ref0, Ref1). More specifically, a difference between(i) a reconstructed image in a specified position in a first encodedreference picture (Ref0) specified by a candidate MV and (ii) areconstructed picture in a specified position in a second encodedreference picture (Ref1) specified by a symmetrical MV scaled at adisplay time interval of the candidate MV may be derived, and theevaluation value for the current block may be calculated by using thederived difference. The candidate MV having the best evaluation valueamong the plurality of candidate MVs may be selected as the final MV.

Under the assumption of continuous motion trajectory, the motion vectors(MV0, MV1) pointing to the two reference blocks shall be proportional tothe temporal distances (TD0, TD1) between the current picture (Cur Pic)and the two reference pictures (Ref0, Ref1). For example, when thecurrent picture is temporally between the two reference pictures and thetemporal distance from the current picture to the two reference picturesis the same, the first pattern matching derives a mirror basedbi-directional motion vector.

In the second pattern matching, pattern matching is performed between atemplate in the current picture (blocks neighboring the current block inthe current picture (for example, the top and/or left neighboringblocks)) and a block in a reference picture. Therefore, in the secondpattern matching, a block neighboring the current block in the currentpicture is used as the predetermined region for the above-describedcalculation of the candidate evaluation value.

FIG. 7 is for illustrating one example of pattern matching (templatematching) between a template in the current picture and a block in areference picture. As illustrated in FIG. 7, in the second patternmatching, a motion vector of the current block is derived by searching areference picture (Ref0) to find the block that best matches neighboringblocks of the current block (Cur block) in the current picture (CurPic). More specifically, a difference between (i) a reconstructed imageof an encoded region that is both or one of the neighboring left andneighboring upper region and (ii) a reconstructed picture in the sameposition in an encoded reference picture (Ref0) specified by a candidateMV may be derived, and the evaluation value for the current block may becalculated by using the derived difference. The candidate MV having thebest evaluation value among the plurality of candidate MVs may beselected as the best candidate MV.

Information indicating whether to apply the FRUC mode or not (referredto as, for example, a FRUC flag) is signalled at the CU level. Moreover,when the FRUC mode is applied (for example, when the FRUC flag is set totrue), information indicating the pattern matching method (first patternmatching or second pattern matching) is signalled at the CU level. Notethat the signaling of such information need not be performed at the CUlevel, and may be performed at another level (for example, at thesequence level, picture level, slice level, tile level, CTU level, orsub-block level).

Here, a mode for deriving a motion vector based on a model assuminguniform linear motion will be described. This mode is also referred toas a bi-directional optical flow (BIO) mode.

FIG. 8 is for illustrating a model assuming uniform linear motion. InFIG. 8, (v_(x), v_(y)) denotes a velocity vector, and τ₀ and τ₁ denotetemporal distances between the current picture (Cur Pic) and tworeference pictures (Ref₀, Ref₁). (MVx₀, MVy₀) denotes a motion vectorcorresponding to reference picture Ref₀, and (MVx₁, MVy₁) denotes amotion vector corresponding to reference picture Ref₁.

Here, under the assumption of uniform linear motion exhibited byvelocity vector (v_(x), v_(y)), (MVx₀, MVy₀) and (MVx₁, MVy₁) arerepresented as (v_(x),≢₀, v_(y)τ₀) and (−v_(x)τ₁, −v_(y)τ₁),respectively, and the following optical flow equation is given.MATH. 1∂I ^((k)) /∂t+v _(x) ∂I ^((k)) /∂x+v _(y) ∂I ^((k)) /∂y=0.   (1)

Here, I^((k)) denotes a luma value from reference picture k (k=0, 1)after motion compensation. This optical flow equation shows that the sumof (i) the time derivative of the luma value, (ii) the product of thehorizontal velocity and the horizontal component of the spatial gradientof a reference picture, and (iii) the product of the vertical velocityand the vertical component of the spatial gradient of a referencepicture is equal to zero. A motion vector of each block obtained from,for example, a merge list is corrected pixel by pixel based on acombination of the optical flow equation and Hermite interpolation.

Note that a motion vector may be derived on the decoder side using amethod other than deriving a motion vector based on a model assuminguniform linear motion. For example, a motion vector may be derived foreach sub-block based on motion vectors of neighboring blocks.

Here, a mode in which a motion vector is derived for each sub-blockbased on motion vectors of neighboring blocks will be described. Thismode is also referred to as affine motion compensation prediction mode.

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks. In FIG. 9A, the currentblock includes 16 4×4 sub-blocks. Here, motion vector v₀ of the top leftcorner control point in the current block is derived based on motionvectors of neighboring sub-blocks, and motion vector v₁ of the top rightcorner control point in the current block is derived based on motionvectors of neighboring blocks. Then, using the two motion vectors v₀ andv₁, the motion vector (v_(x), v_(y)) of each sub-block in the currentblock is derived using Equation 2 below.

$\begin{matrix}{{MATH}.\mspace{14mu} 2} & \; \\\left\{ \begin{matrix}{v_{x} = {{\frac{\left( {v_{1\; x} - v_{0\; x}} \right)}{w}x} - {\frac{\left( {v_{1\; y} - v_{0\; y}} \right)}{w}y} + v_{0\; x}}} \\{v_{y} = {{\frac{\left( {v_{1\; y} - v_{0\; y}} \right)}{w}x} + {\frac{\left( {v_{1\; x} - v_{0\; x}} \right)}{w}y} + v_{0\; y}}}\end{matrix} \right. & (2)\end{matrix}$

Here, x and y are the horizontal and vertical positions of thesub-block, respectively, and w is a predetermined weighted coefficient.

Such an affine motion compensation prediction mode may include a numberof modes of different methods of deriving the motion vectors of the topleft and top right corner control points. Information indicating such anaffine motion compensation prediction mode (referred to as, for example,an affine flag) is signalled at the CU level. Note that the signaling ofinformation indicating the affine motion compensation prediction modeneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, CTU level, or sub-block level).

[Prediction Controller]

Prediction controller 128 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto subtractor 104 and adder 116.

Here, an example of deriving a motion vector via merge mode in a currentpicture will be given. FIG. 9B is for illustrating an outline of aprocess for deriving a motion vector via merge mode.

First, an MV predictor list in which candidate MV predictors areregistered is generated. Examples of candidate MV predictors include:spatially neighboring MV predictors, which are MVs of encoded blockspositioned in the spatial vicinity of the current block; a temporallyneighboring MV predictor, which is an MV of a block in an encodedreference picture that neighbors a block in the same location as thecurrent block; a combined MV predictor, which is an MV generated bycombining the MV values of the spatially neighboring MV predictor andthe temporally neighboring MV predictor; and a zero MV predictor, whichis an MV whose value is zero.

Next, the MV of the current block is determined by selecting one MVpredictor from among the plurality of MV predictors registered in the MVpredictor list.

Furthermore, in the variable-length encoder, a merge_idx, which is asignal indicating which MV predictor is selected, is written and encodedinto the stream.

Note that the MV predictors registered in the MV predictor listillustrated in FIG. 9B constitute one example. The number of MVpredictors registered in the MV predictor list may be different from thenumber illustrated in FIG. 9B, the MV predictors registered in the MVpredictor list may omit one or more of the types of MV predictors givenin the example in FIG. 9B, and the MV predictors registered in the MVpredictor list may include one or more types of MV predictors inaddition to and different from the types given in the example in FIG.9B.

Note that the final MV may be determined by performing DMVR processing(to be described later) by using the MV of the current block derived viamerge mode.

Here, an example of determining an MV by using DMVR processing will begiven.

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing.

First, the most appropriate MVP set for the current block is consideredto be the candidate MV, reference pixels are obtained from a firstreference picture, which is a picture processed in the L0 direction inaccordance with the candidate MV, and a second reference picture, whichis a picture processed in the L1 direction in accordance with thecandidate MV, and a template is generated by calculating the average ofthe reference pixels.

Next, using the template, the surrounding regions of the candidate MVsof the first and second reference pictures are searched, and the MV withthe lowest cost is determined to be the final MV. Note that the costvalue is calculated using, for example, the difference between eachpixel value in the template and each pixel value in the regionssearched, as well as the MV value.

Note that the outlines of the processes described here are fundamentallythe same in both the encoder and the decoder.

Note that processing other than the processing exactly as describedabove may be used, so long as the processing is capable of deriving thefinal MV by searching the surroundings of the candidate MV.

Here, an example of a mode that generates a prediction image by usingLIC processing will be given.

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing.

First, an MV is extracted for obtaining, from an encoded referencepicture, a reference image corresponding to the current block.

Next, information indicating how the luminance value changed between thereference picture and the current picture is extracted and a luminancecorrection parameter is calculated by using the luminance pixel valuesfor the encoded left neighboring reference region and the encoded upperneighboring reference region, and the luminance pixel value in the samelocation in the reference picture specified by the MV.

The prediction image for the current block is generated by performing aluminance correction process by using the luminance correction parameteron the reference image in the reference picture specified by the MV.

Note that the shape of the surrounding reference region illustrated inFIG. 9D is just one example; the surrounding reference region may have adifferent shape.

Moreover, although a prediction image is generated from a singlereference picture in this example, in cases in which a prediction imageis generated from a plurality of reference pictures as well, theprediction image is generated after performing a luminance correctionprocess, via the same method, on the reference images obtained from thereference pictures.

One example of a method for determining whether to implement LICprocessing is by using an lic_flag, which is a signal that indicateswhether to implement LIC processing. As one specific example, theencoder determines whether the current block belongs to a region ofluminance change. The encoder sets the lic_flag to a value of “1” whenthe block belongs to a region of luminance change and implements LICprocessing when encoding, and sets the lic_flag to a value of “0” whenthe block does not belong to a region of luminance change and encodeswithout implementing LIC processing. The decoder switches betweenimplementing LIC processing or not by decoding the lic_flag written inthe stream and performing the decoding in accordance with the flagvalue.

One example of a different method of determining whether to implementLIC processing is determining so in accordance with whether LICprocessing was determined to be implemented for a surrounding block. Inone specific example, when merge mode is used on the current block,whether LIC processing was applied in the encoding of the surroundingencoded block selected upon deriving the MV in the merge mode processingmay be determined, and whether to implement LIC processing or not can beswitched based on the result of the determination. Note that in thisexample, the same applies to the processing performed on the decoderside.

[Decoder Outline]

Next, a decoder capable of decoding an encoded signal (encodedbitstream) output from encoder 100 will be described. FIG. 10 is a blockdiagram illustrating a functional configuration of decoder 200 accordingto Embodiment 1. Decoder 200 is a moving picture/picture decoder thatdecodes a moving picture/picture block by block.

As illustrated in FIG. 10, decoder 200 includes entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, block memory210, loop filter 212, frame memory 214, intra predictor 216, interpredictor 218, and prediction controller 220.

Decoder 200 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, loop filter212, intra predictor 216, inter predictor 218, and prediction controller220. Alternatively, decoder 200 may be realized as one or more dedicatedelectronic circuits corresponding to entropy decoder 202, inversequantizer 204, inverse transformer 206, adder 208, loop filter 212,intra predictor 216, inter predictor 218, and prediction controller 220.

Hereinafter, each component included in decoder 200 will be described.

[Entropy Decoder]

Entropy decoder 202 entropy decodes an encoded bitstream. Morespecifically, for example, entropy decoder 202 arithmetic decodes anencoded bitstream into a binary signal. Entropy decoder 202 thendebinarizes the binary signal. With this, entropy decoder 202 outputsquantized coefficients of each block to inverse quantizer 204.

[Inverse Quantizer]

Inverse quantizer 204 inverse quantizes quantized coefficients of ablock to be decoded (hereinafter referred to as a current block), whichare inputs from entropy decoder 202. More specifically, inversequantizer 204 inverse quantizes quantized coefficients of the currentblock based on quantization parameters corresponding to the quantizedcoefficients. Inverse quantizer 204 then outputs the inverse quantizedcoefficients (i.e., transform coefficients) of the current block toinverse transformer 206.

[Inverse Transformer]

Inverse transformer 206 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 204.

For example, when information parsed from an encoded bitstream indicatesapplication of EMT or AMT (for example, when the AMT flag is set totrue), inverse transformer 206 inverse transforms the transformcoefficients of the current block based on information indicating theparsed transform type.

Moreover, for example, when information parsed from an encoded bitstreamindicates application of NSST, inverse transformer 206 applies asecondary inverse transform to the transform coefficients.

[Adder]

Adder 208 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 206, and prediction samples,which is an input from prediction controller 220. Adder 208 then outputsthe reconstructed block to block memory 210 and loop filter 212.

[Block Memory]

Block memory 210 is storage for storing blocks in a picture to bedecoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 210 storesreconstructed blocks output from adder 208.

[Loop Filter]

Loop filter 212 applies a loop filter to blocks reconstructed by adder208, and outputs the filtered reconstructed blocks to frame memory 214and, for example, a display device.

When information indicating the enabling or disabling of ALF parsed froman encoded bitstream indicates enabled, one filter from among aplurality of filters is selected based on direction and activity oflocal gradients, and the selected filter is applied to the reconstructedblock.

[Frame Memory]

Frame memory 214 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 214 stores reconstructed blocks filtered byloop filter 212.

[Intra Predictor]

Intra predictor 216 generates a prediction signal (intra predictionsignal) by intra prediction with reference to a block or blocks in thecurrent picture and stored in block memory 210. More specifically, intrapredictor 216 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 220.

Note that when an intra prediction mode in which a chroma block is intrapredicted from a luma block is selected, intra predictor 216 may predictthe chroma component of the current block based on the luma component ofthe current block.

Moreover, when information indicating the application of PDPC is parsedfrom an encoded bitstream, intra predictor 216 correctspost-intra-prediction pixel values based on horizontal/verticalreference pixel gradients.

[Inter Predictor]

Inter predictor 218 predicts the current block with reference to areference picture stored in frame memory 214. Inter prediction isperformed per current block or per sub-block (for example, per 4×4block) in the current block. For example, inter predictor 218 generatesan inter prediction signal of the current block or sub-block by motioncompensation by using motion information (for example, a motion vector)parsed from an encoded bitstream, and outputs the inter predictionsignal to prediction controller 220.

Note that when the information parsed from the encoded bitstreamindicates application of OBMC mode, inter predictor 218 generates theinter prediction signal using motion information for a neighboring blockin addition to motion information for the current block obtained frommotion estimation.

Moreover, when the information parsed from the encoded bitstreamindicates application of FRUC mode, inter predictor 218 derives motioninformation by performing motion estimation in accordance with thepattern matching method (bilateral matching or template matching) parsedfrom the encoded bitstream. Inter predictor 218 then performs motioncompensation using the derived motion information.

Moreover, when BIO mode is to be applied, inter predictor 218 derives amotion vector based on a model assuming uniform linear motion. Moreover,when the information parsed from the encoded bitstream indicates thataffine motion compensation prediction mode is to be applied, interpredictor 218 derives a motion vector of each sub-block based on motionvectors of neighboring blocks.

[Prediction Controller]

Prediction controller 220 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto adder 208.

[Deblocking Filtering]

Next, deblocking filtering performed in encoder 100 and decoder 200configured as described above are described specifically with referenceto the drawings. It is to be noted that operations performed by loopfilter 120 included in encoder 100 are mainly described below, and loopfilter 212 included in decoder 200 performs similar operations.

As described above, when encoding an image, encoder 100 calculates aprediction error by subtracting, from an original signal, a predictionsignal which is generated by intra predictor 124 or inter predictor 126.Encoder 100 generates quantized coefficients by performing an orthogonaltransform process and a quantization process on a prediction error.Furthermore, encoder 100 restores the prediction error by performinginverse quantization and inverse orthogonal transform on the resultingquantized coefficients. Here, a quantization process is irreversibleprocessing, and thus the restored prediction error has an error(quantization error) from the pre-transform prediction error.

Deblocking filtering performed by loop filter 120 is a kind of filteringperformed with an aim to reduce the quantization error. Deblockingfiltering is applied to block boundaries to remove block noise. It is tobe noted that deblocking filtering is also simply referred to asfiltering hereinafter.

FIG. 11 is a flowchart indicating an example of deblocking filteringperformed by loop filter 120. For example, processing indicated in FIG.11 is performed for each of block boundaries.

First, loop filter 120 calculates a block boundary strength (Bs) inorder to determine a behavior of deblocking filtering (S101). Morespecifically, loop filter 120 determines a Bs using a prediction mode ofa block to be a target of a filter or a property of a motion vector. Forexample, Bs=2 is set when at least one of blocks across a boundary is anintra prediction block. In addition, Bs=1 is set when at least one ofthe following conditions (1) to (3) is satisfied: (1) at least one ofblocks across a boundary includes a higher orthogonal transformcoefficient; (2) the difference between motion vectors of both blocksacross a boundary is larger than or equal to a threshold value; and (3)the numbers of motion vectors or reference images of both blocks acrossa boundary are different from each other. Bs=0 is set when none of theconditions (1) to (3) is satisfied.

Next, loop filter 120 determines whether the set Bs is larger than afirst threshold value (S102). When Bs is smaller than or equal to thefirst threshold value (No in S102), loop filter 120 does not performfiltering (S107).

When the set Bs is larger than the first threshold value (Yes in S102),loop filter 120 calculates a pixel difference d in a boundary area,using pixel values of blocks located at both sides of a block boundary(S103). This processing is described with reference to FIG. 12. When thepixel values at the block boundary are defined as in FIG. 12, loopfilter 120 calculates, for example,d=|p30·2×p20+p10|+|p33·2×p23+p13|+|q30·2×q20+q10|+|q33−2×q23+q13|.

Next, loop filter 120 determines whether the calculated d is larger thana second threshold value (S104). When the calculated d is smaller thanor equal to the second threshold value (No in S104), loop filter 120does not perform filtering (S107). It is to be noted that the firstthreshold value is different from the second threshold value.

When the calculated d is larger than the second threshold value (Yes inS104), loop filter 120 determines a filter characteristic (S105), andperforms filtering using the determined filter characteristic (S106).For example, a 5-tap filter of (1, 2, 2, 2, 1)/8 is used. Specifically,for p10 indicated in FIG. 12, a calculation of(1×p30+2×p20+2×p10+2×q10+1×q20)/8 is performed. Here, in the filtering,clipping is performed so that variation falls within a certain rangewithout excessive smoothing. Clipping here is threshold processingwhich, for example, when a threshold value for clipping is tc and apixel value to be filtered is q, only allows the filtered pixel value totake a value within the range of q±tc.

Hereinafter, a description is given of an example of applying anasymmetrical filter across a block boundary in deblocking filteringperformed by loop filter 120 according to this embodiment.

FIG. 13 is a flowchart indicating an example of deblocking filteringaccording to this embodiment. It is to be noted that the processingindicated in FIG. 13 may be performed for each block boundary, or foreach unit of one or more pixels.

First, loop filter 120 obtains a coding parameter, and determines anasymmetrical filter characteristic across a boundary, using the obtainedcoding parameter (S111). In the present disclosure, the obtained codingparameter is assumed to, for example, characterize an errordistribution.

Here, filter characteristics are filter coefficients and parameters,etc. used to control filtering. In addition, a coding parameter may beany parameter which can be used to determine a filter characteristic. Acoding parameter may be information indicating an error per se, or maybe information or a parameter (which, for example, affects the magnitudeof the error) related to the error.

In addition, hereinafter, a pixel which has been determined to have alarge or small error based on a coding parameter, that is, a pixel whichis more likely to have a large or small error is also simply referred toas a pixel having a large or small error.

Here, a determination process does not need to be performed each time,and a process may be performed according to a predetermined rule whichassociates a coding parameter and a filter characteristic.

It is to be noted that, when each pixel is seen, even a pixel which isstatistically more likely to have a small error may have an error largerthan an error of a pixel which is more likely to have a large error.

Next, loop filter 120 executes filtering using the determined filtercharacteristic (S112).

Here, a filter characteristic determined in Step S111 does not alwaysneed to be asymmetrical, and can be designed to be symmetrical. It is tobe noted that, hereinafter, a filter having an asymmetrical filtercharacteristic across a block boundary is also referred to as anasymmetrical filter, and a filter having a symmetrical filtercharacteristic across a block boundary is also referred to as asymmetrical filter.

More specifically, the filter characteristic is determined consideringthe following two points that: a pixel determined to have a small erroris less affected by a neighboring pixel having a large error; and thepixel determined to have the large error is more affected by theneighboring pixel having the small error. In other words, the filtercharacteristic is determined such that a pixel having a larger error ismore affected by filtering. In other words, a filter characteristic isdetermined such that the pixel value of a pixel having a larger error ischanged by a larger amount before and after filtering. In this way, asfor a pixel which is more likely to have a small error, it is possibleto prevent the pixel from departing from a true value by a large changein value. As for the pixel which is more likely to have the large error,it is possible to reduce the error of the pixel by changing the valueafter being more affected by the pixel having the small error.

It is to be noted that an element which changes variation by a filer isdefined as a weight of a filter. In other words, a weight indicates adegree of influence of filtering on a current pixel. Increasing a weightmeans increasing influence of filtering on the pixel. In other words,increasing a weight means that a filtered pixel value is more affectedby another pixel. More specifically, increasing a weight meansdetermining a filter characteristic so that the pixel value of a pixelcan be changed by a larger amount before and after filtering, orfiltering is likely to be performed.

In other words, loop filter 120 increases the weight of a pixel having alarger error more significantly. It is to be noted that increasing theweight of a pixel having a larger error more significantly is notlimited to changing the weight continuously and includes changing theweight stepwise. In other words, it is only necessary that the weight ofa first pixel is smaller than the weight of a second pixel having alarger error than the first pixel. In addition, similar expressions arealso used below.

It is to be noted that a pixel having a larger error does not need tohave a larger weight in a finally determined filtering characteristic.In other words, for example, it is only necessary for loop filter 120 tochange a filter characteristic which becomes a reference determinedaccording to a conventional approach to have a tendency that a pixelhaving a larger error has a larger weight.

Hereinafter, a plurality of specific approaches for changing weightsasymmetrically are described. It is to be noted that any of theapproaches indicated below may be used, or a combination of a pluralityof approaches may be used.

As a first approach, loop filter 120 decreases a filter coefficient moresignificantly for a pixel having a larger error. For example, loopfilter 120 decreases a filter coefficient for a pixel having a largeerror, and increases a filter coefficient for a pixel having a smallerror.

For example, a description is given of an example of deblockingfiltering performed on pixel p1 indicated in FIG. 12. This approach isnot applied hereinafter, and, for example, a filter determined accordingto a conventional approach is referred to as a reference filter. It isassumed that the reference filter is a 5-tap filter vertical to a blockboundary, and is set for (p3, p2, p1, q1, q2). In addition, a filtercoefficient is determined to be (1, 2, 2, 2, 1)/8. In addition, it isassumed that an error of block P is more likely to be large, and that anerror of block Q is more likely to be small. In this way, a filtercoefficient is set so that block P having a large error is more affectedby block Q having a small error.

More specifically, a filter coefficient used for a pixel having a smallerror is set to be large, and a filter coefficient used for a pixelhaving a large error is set to be small. For example, as a filtercoefficient, (0.5, 1.0, 1.0, 2.0, 1.5)/6 is used.

As another example, 0 is used as a filter coefficient for a pixel havinga small error. For example, (0, 0, 1, 2, 2)/5 may be used as a filtercoefficient. In other words, a filter tap may be changed. A filtercoefficient which is currently 0 may be set to a value other than 0. Forexample, (1, 2, 2, 2, 1, 1)/9 may be used as a filter coefficient. Inother words, loop filter 120 may increase the number of filter taps at asmall error side.

It is to be noted that a reference filter is not a filter which ishorizontally symmetrical about a current pixel as in the case of (1, 2,2, 2, 1)/8 described above. In such a case, loop filter 120 furtheradjusts the filter. For example, the filter coefficient for a referencefilter to be used for a left-end pixel in block Q is (1, 2, 3, 4, 5)/15,and the filter coefficient for a reference filter to be used for aright-end pixel in block P is (5, 4, 3, 2, 1)/15. In other words, inthis case, the reverse-landscape filter coefficients are used betweenthe pixels across the block boundary. Such a filter characteristic whichis reverse-symmetrical across a block boundary can be said to be “afilter characteristic which is symmetrical across a block boundary”. Inother words, a filter characteristic which is asymmetrical across ablock boundary is a filter characteristic which is notreverse-symmetrical across a block boundary.

In addition, similarly to the above, when block P has a large error andblock Q has a small error, loop filter 120 changes, for example, (5, 4,3, 2, 1)/15 which is the filter coefficient for a reference filter to beused for a right-end pixel in block P to (2.5, 2.0, 1.5, 2.0, 1.0)/9.

In this way, in deblocking filtering, a filter having filtercoefficients which change asymmetrically across a block boundary areused. For example, loop filter 120 determines a reference filter havingfilter coefficients which are symmetrical across a boundary according toa predetermined reference. Loop filter 120 changes the reference filterto have filter coefficients which are asymmetrical across a boundary.More specifically, loop filter 120 performs at least one of: increasinga filter coefficient of at least one pixel having a small error amongthe filter coefficients of the reference filter; and decreasing a filtercoefficient of at least one pixel having a large error among the filtercoefficients of the reference filter.

Next, a second approach for changing weights asymmetrically isdescribed. First, loop filter 120 performs a filter calculation using areference filter. Next, loop filter 120 performs asymmetrical weightingacross a block boundary onto reference change amount Δ0 which is theamount of change in pixel value before and after the filter calculationusing a reference filter. It is to be noted that, hereinafter, fordistinction, processing using a reference filter is referred to as afilter calculation, and sequential processing including a filtercalculation and subsequent correction (for example, asymmetricalweighting) is referred to as filtering (deblocking filtering).

For example, in the case of a pixel having a small error, loop filter120 calculates corrected change amount Δ0 by multiplying referencechange amount Δ0 with a coefficient smaller than 1. In addition, in thecase of a pixel having a large error, loop filter 120 calculates acorrected change amount Δ0 by multiplying reference change amount Δ0with a coefficient larger than 1. Next, loop filter 120 generates afiltered pixel value by adding a pixel value before a filter calculationto corrected change amount Δ1. It is to be noted that loop filter 120may perform only one of processing on the pixel having a small error andprocessing on the pixel having a large error.

For example, similarly to the above, it is assumed that block P has alarge error and block Q has a small error. In this case, in the case ofa pixel included in block Q having a small error, loop filter 120calculates corrected change amount Δ1 by, for example, multiplyingreference change amount Δ0 by 0.8. In addition, in the case of a pixelincluded in block P having a large error, loop filter 120 calculatescorrected change amount Δ1 by, for example, multiplying reference changeamount Δ0 by 1.2. In this way, it is possible to decrease variation inpixel value having a small error. In addition, it is possible toincrease variation in pixel value having a large error.

It is to be noted that 1:1 may be selected as a ratio between acoefficient that is multiplied with reference change amount Δ0 of apixel having a small error and a coefficient that is multiplied withreference change amount Δ0 having a large error. In this case, thefilter characteristic is symmetrical across a block boundary.

In addition, loop filter 120 may calculate a coefficient that ismultiplied with reference change amount Δ0 by multiplying the referencecoefficient by a constant. In this case, loop filter 120 uses a largerconstant for a pixel having a large error than a constant for a pixelhaving a small error. As a result, the change amount in pixel value ofthe pixel having the large error increases, and the change amount inpixel value of the pixel which is more likely to have the small errordecreases. For example, loop filter 120 uses 1.2 or 0.8 as a constantfor a pixel that neighbors a block boundary, and uses 1.1 or 0.9 as aconstant for a pixel that is apart by one pixel from the pixel thatneighbors the block boundary. In addition, a reference coefficient iscalculated according to, for example, (A×(q1−p1)−B×(q2−p2)+C)/D. Here,A, B, C, and D are constants. For example, A=9, B=3, C=8, and D=16 aresatisfied. In addition, p1, p2, q1, and q2 are pixel values of pixelslocated across a block boundary and are in a positional relationshipindicated in FIG. 12.

Next, a third approach for changing weights asymmetrically is described.Loop filter 120 performs a filter calculation using a filter coefficientof a reference filter similarly to the second approach. Next, loopfilter 120 adds asymmetrical offset values to pixel values after beingsubjected to the filter calculation across a block boundary. Morespecifically, loop filter 120 adds a positive offset value to a pixelvalue of a pixel having a large error so that the value of the pixelhaving the large error is made closer to the value of pixel which ismore likely to have a small error and the variation of the pixel havingthe large error becomes large. In addition, loop filter 120 adds anegative offset value to the pixel value of the pixel having the smallerror so that the value of the pixel having the small error is not madecloser to the value of the pixel having the large error and thevariation of the pixel having the small error becomes small. As aresult, the change amount in pixel value of the pixel having the largeerror increases, and the change amount in pixel value of the pixelhaving the small error decreases. It is to be noted that loop filter 120may perform only one of processing on the pixel having a small error andprocessing on the pixel having a large error.

For example, for a pixel included in a block having a large error, loopfilter 120 calculates corrected change amount Δ1 by adding a positiveoffset value (for example, 1) to the absolute value of reference changeamount Δ0. In addition, for a pixel included in a block having a smallerror, loop filter 120 calculates corrected change amount Δ1 by adding anegative offset value (for example, −1) to the absolute value ofreference change amount Δ0. Next, loop filter 120 generates a filteredpixel value by adding corrected change amount Δ1 to the pixel valuebefore being subjected to the filter calculation. It is to be noted thatloop filter 120 may add an offset value to the filtered pixel valueinstead of adding an offset value to a change amount. In addition, theoffset values may not be symmetrical across a block boundary.

In addition, when a filter tap is set for a plurality of pixelsneighboring a block boundary, loop filter 120 may change only theweights for particular pixels or may change the weights for all thepixels. In addition, loop filter 120 may change the weights of thetarget pixels according to the distances from the block boundary to thetarget pixels. For example, loop filter 120 may make filter coefficientsfor two pixels from a block boundary asymmetrical, and make the otherfilter coefficients for subsequent pixels symmetrical. In addition,filter weights may be common to a plurality of pixels, or may be set foreach pixel.

Next, a fourth approach for changing weights asymmetrically isdescribed. Loop filter 120 performs a filter calculation using a filtercoefficient of a reference filter. Next, when a change amount A in pixelvalue before and after the filter calculation exceeds a clip width whichis a reference value, loop filter 120 clips the change amount A to theclip width. Loop filter 120 sets asymmetrical clip widths across a blockboundary.

Specifically, loop filter 120 makes a clip width for a pixel having alarge error wider than the clip width of a pixel having a small error.For example, loop filter 120 makes the clip width for the pixel havingthe large error to a constant multiple of the clip width for the pixelhaving the smaller error. As a result of changing the clip width, thevalue of the pixel having the small error is prohibited from changingsignificantly. In addition, the value of the pixel having the largeerror is allowed to change significantly.

It is to be noted that loop filter 120 may adjust the absolute values ofthe clip widths instead of specifying a clip width ratio. For example,loop filter 120 fixes the clip width for a pixel having a large error ata multiple of a predetermined reference clip width. Loop filter 120 setsthe ratio between the clip width for the pixel having the large errorand the clip width for a pixel having a small error to 1.2:0.8.Specifically, for example, it is assumed that the reference clip widthis 10, and that the change amount A before and after a filtercalculation is 12. In this case, in the case where the reference clipwidth is used as it is, the change amount A is corrected to 10 bythreshold processing. In the opposite case where a target pixel is apixel having a large error, the reference clip width is multiplied by,for example, 1.5. In this way, since the clip width becomes 15, nothreshold processing is performed, and the change amount Δ is 12.

Next, a fifth approach for changing weights asymmetrically is described.Loop filter 120 sets an asymmetrical condition for determining whetherto perform filtering across a block boundary. Here, the condition fordetermining whether to perform filtering is, for example, a firstthreshold value or a second threshold value indicated in FIG. 11.

More specifically, loop filter 120 sets a condition for increasing thelikeliness of filtering on a pixel having a large error and a conditionfor decreasing the likeliness of filtering on a pixel having a smallerror. For example, loop filter 120 sets a higher threshold value for apixel having a small error than a threshold value for a pixel having alarge error. For example, loop filter 120 sets the threshold value forthe pixel having the small error to be a constant multiple of thethreshold value for the pixel having the large error.

In addition, loop filter 120 may adjust the absolute values of thethreshold values not only specifying the threshold value ratio. Forexample, loop filter 120 may fix a threshold value for a pixel having asmall error to a multiple of a predetermined reference threshold value,and may set the ratio between the threshold value for the pixel havingthe small error and a threshold value for a pixel having a large errorto be 1.2:0.8.

Specifically, it is assumed that a reference threshold value for asecond threshold value in Step S104 is 10, and that the d calculatedfrom the pixel value in a block is 12. In the case where the referencethreshold value is used as the second threshold value as it is, it isdetermined that filtering is performed. In the opposite case where atarget pixel is a pixel having a small error, for example, a valueobtained by multiplying the reference threshold value by 1.5 is used asthe second threshold value. In this case, the second threshold valuebecomes 15 which is larger than d. In this way, it is determined that nofiltering is performed.

In addition, constants, etc. indicating weights based on errors used inthe above-described first to fifth approaches may be valuespredetermined in encoder 100 and decoder 200, or may be variable.Specifically, these constants include: a filter coefficient or acoefficient that is multiplied with a filter coefficient of a referencefilter in the first approach; a coefficient that is multiplied withreference change amount AO or a constant that is multiplied with areference coefficient in the second approach; an offset value in thesecond approach; a clip width or a constant multiplied with a referenceclip width in the fourth approach; and a threshold value or a constantthat is multiplied with a reference threshold value in the fifthapproach.

When a constant is variable, information indicating the constant may beincluded in a bitstream as a parameter in units of a sequence or aslice, and may be transmitted from encoder 100 to decoder 200. It is tobe noted that the information indicating the constant may be informationindicating the constant as it is, or may be information indicating aratio with or a difference from a reference value.

In addition, according to errors, as methods for changing coefficientsor constants, for example, there are a method for changing themlinearly, a method for changing them quadratically, a method forchanging them exponentially, a method using a look-up table indicatingthe relationships between errors and constants, or other methods.

In addition, when an error is larger than or equal to a reference, orwhen an error is smaller than or equal to a reference, a fixed value maybe used as a constant. For example, loop filter 120 may set a variableto a first value when an error is below a predetermined range, may set avariable to a second value when an error is above the predeterminedrange, or may change a variable to a continuous variable according to anerror, in a range from the first value to the second value when theerror is within the predetermined range.

In addition, when an error exceeds a predetermined reference, loopfilter 120 may use a symmetrical filter (reference filter) without usingan asymmetrical filter.

In addition, in the case of using a look-up table, etc, loop filter 120may hold tables for both a case where an error is large and a case wherean error is small, or may hold only one of the tables and may calculatea constant for the other according to a rule predetermined based on thecontent of the table.

As described above, encoder 100 and decoder 200 according to thisembodiment are capable of reducing errors in a reconstructed image byusing an asymmetrical filter, and thereby increasing coding efficiency.

This aspect may be implemented in combination with one or more of theother aspects according to the present disclosure. In addition, part ofthe processes in the flowcharts, part of the constituent elements of theapparatuses, and part of the syntax described in this aspect may beimplemented in combination with other aspects.

Embodiment 2

Embodiments 2 to 6 describe specific examples of coding parameters whichcharacterize the above-described error distributions. In thisembodiment, loop filter 120 determines a filter characteristic accordingto the position of a current pixel in a block.

FIG. 14 is a flowchart indicating an example of deblocking filteringaccording to this embodiment. First, loop filter 120 obtains informationindicating the position of the current pixel in a block, as a codingparameter which characterizes an error distribution. Loop filter 120determines an asymmetrical filter characteristic across a block boundarybased on the position (S121).

Next, loop filter 120 executes filtering using the determined filtercharacteristic (S122).

Here, a pixel distant from a reference pixel in intra prediction is morelikely to have a large error than a pixel close to the reference pixelin intra prediction. Accordingly, loop filter 120 determines the filtercharacteristic so that the pixel value of the pixel more distant fromthe reference pixel in intra prediction changes by a larger changeamount before and after filtering.

For example, in the case of H.265/HEVC or JEM, as indicated in FIG. 15,a pixel close to a reference pixel is a pixel present at an upper-leftpart of a block, and a pixel distant from a reference pixel is a pixelpresent at a lower-right part of the block. Accordingly, loop filter 120determines the filter characteristic so that the weight for thelower-right pixel in the block becomes larger than the weight for theupper-left pixel.

Specifically, loop filter 120 determines the filter characteristic sothat the pixel distant from the reference pixel in intra prediction ismore affected by filtering as described in Embodiment 1. In other words,loop filter 120 increases the weight for the pixel distant from thereference pixel in intra prediction. Here, as described above,increasing a weight is performing at least one of: (1) decreasing afilter coefficient; (2) increasing a filter coefficient for a pixelacross a boundary (that is, a pixel close to a reference pixel in intraprediction); (3) increasing a coefficient which is multiplied with achange amount; (4) increasing an offset value for a change amount; (5)increasing a clip width; and (6) changing a threshold value so as toincrease the likeliness of filtering. As for the pixel close to thereference pixel in intra prediction, loop filter 120 determines a filtercharacteristic so that the pixel is less affected by filtering. In otherwords, loop filter 120 decreases the weight for the pixel close to thereference pixel in intra prediction. Here, as described above,decreasing a weight is performing at least one of: (1) increasing afilter coefficient; (2) decreasing a filter coefficient for a pixelacross a boundary (that is, a pixel close to a reference pixel in intraprediction); (3) decreasing a coefficient which is multiplied with achange amount; (4) decreasing an offset value for a change amount; (5)decreasing a clip width; and (6) changing a threshold value so as todecrease the likeliness of filtering.

It is to be noted that the above processing may be performed when intraprediction is used, and may not by performed for a block for which interprediction is used. However, since the property of an intra predictionblock may have an influence in inter prediction, the above-describedprocessing may be performed also on an inter prediction block.

In addition, loop filter 120 may change weights by arbitrarilyspecifying positions in a particular block. For example, loop filter 120may increase the weight of a lower-right pixel in a block and decreasethe weight of an upper-left pixel in the block as described above. It isto be noted that loop filter 120 may change weights by arbitrarilyspecifying positions other than the upper-left and lower-right positionsin the particular block.

In addition, as indicated in FIG. 15, left-side blocks have a largeerror and right-side blocks have a small error at the boundaries ofhorizontally neighboring blocks. Thus, loop filter 120 may increase theweights for the left-side blocks and decrease the weights for theright-side blocks at the boundaries of horizontally neighboring blocks.

Likewise, at the boundaries of vertically neighboring blocks, upper-sideblocks have a large error, and lower-side blocks have a small error.Thus, loop filter 120 may increase the weights for the upper-side blocksand decrease the weights for the lower-side blocks at the boundaries ofvertically neighboring blocks.

In addition, loop filter 120 may change weights according to thedistances from a reference pixel in intra prediction. In addition, loopfilter 120 may determine weights in units of a block boundary, or maydetermine weights in units of a pixel. Errors are likely to be largewith increase in distance from a reference pixel. Thus, loop filter 120determines a filter characteristic so that the gradient of weightsbecomes sharp with increase in distance from the reference pixel. Inaddition, loop filter 120 determines the filter characteristic so thatthe weight gradient in the upper side of the right side of a block isgentler than the weight gradient in the lower side thereof.

This aspect may be implemented in combination with one or more of theother aspects according to the present disclosure. In addition, part ofthe processes in the flowcharts, part of the constituent elements of theapparatuses, and part of the syntax described in this aspect may beimplemented in combination with other aspects.

Embodiment 3

In this embodiment, loop filter 120 determines a filter characteristicaccording to an orthogonal transform basis.

FIG. 16 is a flowchart indicating an example of deblocking filteringaccording to this embodiment. First, loop filter 120 obtains informationindicating orthogonal transform basis used for a current block, as acoding parameter which characterizes an error distribution. Loop filter120 determines an asymmetrical filter characteristic across a blockboundary based on the orthogonal transform basis (S131).

Next, loop filter 120 executes filtering using the determined filtercharacteristic (S132).

Encoder 100 selects an orthogonal transform basis which is a transformbasis at the time when orthogonal transform is performed, from aplurality of candidates. The plurality of candidates include, forexample, a flat basis whose zero-order transform basis is flat such asDCT-II, or the like, and a basis whose zero-order transform basis is notflat such as DST-VII, or the like. FIG. 17 is a diagram indicating aDCT-II transform basis. FIG. 18 is a diagram indicating a DCT-VIItransform basis.

The zero-order basis in DCT-II is constant regardless of the positionsin a block. In other words, when DCT-II is used, errors in the blocksare constant. Thus, when both blocks across a block boundary have beentransformed using DCT-II, loop filter 120 performs filtering using asymmetrical filter without using an asymmetrical filter.

In contrast, the value of the zero-order basis in DST-VII becomes largewith increase in distance from a left or upper block boundary. In otherwords, errors are more likely to be large with increase in distance fromthe left or upper block boundary. Thus, loop filter 120 uses anasymmetrical filter when at least one of the two blocks across a blockboundary has been transformed using DST-VII. Specifically, loop filter120 determines a filter characteristic so that a pixel having a smallervalue of a lower-order (for example, zero-order) basis in a block isless affected by filtering.

More specifically, when both blocks across a block boundary have beentransformed using DST-VII, loop filter 120 determines the filtercharacteristic so that a lower-right pixel in the block is more affectedby filtering according to the above-described approach. In addition,loop filter 120 determines the filter characteristic so that anupper-left pixel in the block is less affected by filtering.

In addition, also when a block for which DST-VII has been used and ablock for which DCT-II has been used neighbor vertically, loop filter120 determines a filter characteristic so that a filter weight for apixel in the lower part of the upper block for which DST-VII has beenused and which neighbors a block boundary becomes larger than a filterweight for a pixel in the upper part of the lower block for which DCT-IIhas been used and which neighbors the block boundary. However, thedifference in the amplitude of a low-order basis in this case is smallerthan the difference in the amplitude of the lower-order basis whenblocks for which DST-VII has been used neighbor each other. Thus, loopfilter 120 sets a filter characteristic so that the weight gradient inthis case becomes smaller than the weight gradient in the case whereblocks for which DST-VII has been used neighbor each other. For example,loop filter 120 sets the weights in the case where a block for whichDCT-II has been used and a block for which DCT-II has been used neighborvertically to 1:1 (a symmetrical filter), the weights in the case wherea block for which DST-VII has been used and a block for which DST-VIIhas been used neighbor vertically to 1.3:0.7, and the weights in thecase where a block for which DST-VII has been used and a block for whichDCT-II has been used neighbor vertically to 1.2:0.8.

This aspect may be implemented in combination with one or more of theother aspects according to the present disclosure. In addition, part ofthe processes in the flowcharts, part of the constituent elements of theapparatuses, and part of the syntax described in this aspect may beimplemented in combination with other aspects.

Embodiment 4

In this embodiment, loop filter 120 determines a filter characteristicaccording to the pixel values of pixels across a block boundary.

FIG. 19 is a flowchart indicating an example of deblocking filteringaccording to this embodiment. First, loop filter 120 obtains informationindicating the pixel values of pixels in blocks across a boundary, as acoding parameter which characterizes an error distribution. Loop filter120 determines an asymmetrical filter characteristic across the blockboundary based on the pixel values (S141).

Next, loop filter 120 executes filtering using the determined filtercharacteristic (S142).

For example, loop filter 120 increases the difference in filtercharacteristic across a block boundary with increase in difference d0 inpixel value. Specifically, loop filter 120 determines a filtercharacteristic so that the difference in influence by filtering becomeslarge. For example, loop filter 120 sets weights to 1.4:0.6 whend0>(quantization parameter) x (constant) is satisfied, and sets weightsto 1.2:0.8 when d0>(quantization parameter) x (constant) is notsatisfied. In other words, loop filter 120 compares difference d0 inpixel value and a threshold value based on a quantization parameter, andwhen difference d0 in pixel value is larger than the threshold value,increases the difference in filter characteristic across the blockboundary so that the difference becomes larger than when difference d0in pixel value is smaller than the threshold value.

As another example, loop filter 120 increases the difference in filtercharacteristic across a block boundary with increase in average value b0of variance in pixel value in both blocks across the boundary.Specifically, loop filter 120 may determine a filter characteristic sothat the difference in influence by filtering becomes large. Forexample, loop filter 120 sets weights to 1.4:0.6 when b0>(quantizationparameter) x (constant) is satisfied, and sets weights to 1.2:0.8 whenb0>(quantization parameter) x (constant) is not satisfied. In otherwords, loop filter 120 compares variance b0 in pixel value and athreshold value based on a quantization parameter, and when variance b0in pixel value is larger than the threshold value, increases thedifference in filter characteristic across the block boundary so thatthe difference becomes larger than when variance b0 in pixel value issmaller than the threshold value.

It is to be noted that the block whose weight is to be increased amongneighboring blocks, that is, the block having a larger error can beidentified according to the approach of Embodiment 2 or 3 describedabove or approaches, etc. according to Embodiment 6 to be describedlater. In other words, loop filter 120 determines an asymmetrical filtercharacteristic across a block boundary according to a predetermined rule(for example, the approach according to Embodiment 2, 3, or 6). Next,loop filter 120 changes the determined filter characteristic so that thedifference in filter characteristic across the block boundary becomeslarge based on difference d0 in pixel values. In other words, loopfilter 120 increases the ratio or difference between the weight for apixel having a large error and the weight for a pixel having a smallerror.

Here, when difference d0 in pixel value is large, there is a possibilitythat a block boundary coincides with the edge of an object in an image.In such a case, it is possible to reduce unnecessary smoothing bydecreasing the difference in filter characteristic across the blockboundary.

On the contrary, it is to be noted that loop filter 120 may decrease thedifference in filter characteristic across the block boundary withincrease in difference d0 in pixel value. Specifically, loop filter 120determines a filter characteristic so that the difference in influenceby filtering becomes small. For example, loop filter 120 sets weights to1.2:0.8 when d0>(quantization parameter) x (constant) is satisfied, andsets weights to 1.4:0.6 when d0>(quantization parameter) x (constant) isnot satisfied. It is to be noted that the weights may be set to 1:1(symmetrical filter) when the above relationship is satisfied. In otherwords, loop filter 120 compares difference d0 in pixel value and athreshold value based on a quantization parameter, and when differenced0 in pixel value is larger than the threshold value, decreases thedifference in filter characteristic across the block boundary so thatthe difference becomes smaller than when difference d0 in pixel value issmaller than the threshold value. For example, when difference d0 inpixel value is large, a block boundary tends to be noticeable. In such acase, it is possible to reduce weakening of smoothing by an asymmetricalfilter by decreasing the difference in filter characteristic across theblock boundary.

It is to be noted that these two processes may be performed at the sametime. For example, loop filter 120 may use a first weight whendifference d0 in pixel value is less than a first threshold value, usesa second weight for a larger difference than the difference for whichthe first weight is used, when difference d0 in pixel value is largerthan or equal to the first threshold value and less than the secondthreshold value, and uses a third weight for a smaller difference thanthe difference for which the second weight is used, when difference d0in pixel value is larger than or equal to the second threshold value.

In addition, difference d0 in pixel value may be the difference per sebetween pixel values of pixels across a boundary, or the average orvariance of the differences between the pixel values of the pixels. Forexample, difference d0 in pixel value is calculated according to(A×(q1−p1)·B×(q2−p2)+C)/D. Here, A, B, C, and D are constants. Forexample, A=9, B=3, C=8, and D=16 are satisfied. In addition, p1, p2, q1,and q2 are pixel values of pixels located across a block boundary andare in a positional relationship indicated in FIG. 12.

It is to be noted that difference d0 in pixel value and weights forpixels may be set in units of a pixel, in units of a block boundary, orin units of a block group including a plurality of blocks (for example,in units of a largest coding unit (LCU)).

This aspect may be implemented in combination with one or more of theother aspects according to the present disclosure. In addition, part ofthe processes in the flowcharts, part of the constituent elements of theapparatuses, and part of the syntax described in this aspect may beimplemented in combination with other aspects.

Embodiment 5

In this embodiment, loop filter 120 determines a filter characteristicaccording to an intra prediction direction and a block boundarydirection.

FIG. 20 is a flowchart indicating an example of deblocking filteringaccording to this embodiment. First, loop filter 120 obtains informationindicating an angle between the intra prediction direction and the blockboundary, as a coding parameter which characterizes an errordistribution. Loop filter 120 determines an asymmetrical filtercharacteristic across a block boundary, based on the angle (S151).

Next, loop filter 120 executes filtering using the determined filtercharacteristic (S152).

Specifically, loop filter 120 increases the difference in filtercharacteristic across a block boundary more significantly as the angleis closer to the vertical axis, and decreases the difference in filtercharacteristic across a block boundary more significantly as the angleis closer to the horizontal axis. More specifically, loop filter 120determines the filter characteristic so that the difference betweenfilter weights for pixels at both sides across a block boundary becomeslarge when the intra prediction direction is close to the vertical axisrelative to the block boundary, and the difference between filterweights for pixels at both sides across a block boundary becomes smallwhen the intra prediction direction is close to the horizontal axisrelative to the block boundary. FIG. 21 is a diagram indicating examplesof weights for relationships between intra prediction directions andblock boundary directions.

It is to be noted that the block whose weight is to be increased amongneighboring blocks, that is, the block having a larger error can beidentified according to the approach of Embodiment 2 or 3 describedabove or approaches, etc. according to Embodiment 6 to be describedlater. In other words, loop filter 120 determines an asymmetrical filtercharacteristic across a block boundary according to a predetermined rule(for example, the approach according to Embodiment 2, 3, or 6). Next,loop filter 120 changes the determined filter characteristic so that thedifference in filter characteristic across the block boundary becomeslarge based on the intra prediction direction and the block boundarydirection.

In addition, encoder 100 and decoder 200 identify the intra predictiondirection using, for example, an intra prediction mode.

It is to be noted that when the intra prediction mode is Planner mode orDC mode, loop filter 120 does not always need to consider the blockboundary direction. For example, when the intra prediction mode isPlanar mode or DC mode, loop filter 120 may use a predetermined weightor the difference in weight regardless of the block boundary direction.Alternatively, loop filter 120 may use a symmetrical filter when theintra prediction mode is Planar mode or DC mode.

This aspect may be implemented in combination with one or more of theother aspects according to the present disclosure. In addition, part ofthe processes in the flowcharts, part of the constituent elements of theapparatuses, and part of the syntax described in this aspect may beimplemented in combination with other aspects.

Embodiment 6

In this embodiment, loop filter 120 determines a filter characteristicaccording to a quantization parameter indicating a quantization width.

FIG. 22 is a flowchart indicating an example of deblocking filteringaccording to this embodiment. First, loop filter 120 obtains informationindicating the quantization parameter used in the quantization of acurrent block, as a coding parameter which characterizes an errordistribution. Loop filter 120 determines an asymmetrical filtercharacteristic across a block boundary, based on the quantizationparameter (S161).

Next, loop filter 120 executes filtering using the determined filtercharacteristic (S162).

Here, an error is more likely to be large when a quantization parameteris larger. Thus, loop filter 120 determines a filter characteristic sothat influence of filtering becomes large as the quantization parameterbecomes larger.

FIG. 23 is a diagram indicating an example of weights for quantizationparameters. As shown in FIG. 23, loop filter 120 increases the weightfor the upper-left pixel in a block with increasing quantizationparameter. On the contrary, loop filter 120 decreases the weight for thelower-right pixel in the block with increasing quantization parameter.In other words, loop filter 120 determines a filter characteristic sothat change in influence of filtering using changing quantizationparameter for the upper-left pixel becomes larger than change ininfluence of filtering using changing quantization parameter for thelower-right pixel.

Here, the upper-left pixel in the block is more likely to be affected bya quantization parameter than the lower-right pixel in the block. Thus,it is possible to reduce errors appropriately by performing theprocessing as described above.

In addition, loop filter 120 may determine, for each of two blocksacross a boundary, a weight for the block based on the quantizationparameter for the block, or may calculate an average value ofquantization parameters for the two blocks and determine weights for thetwo blocks based on the average value. Alternatively, loop filter 120may determine weights for the two blocks based on the quantizationparameter for one of the blocks. For example, loop filter 120 determinesa weight for the one block based on the quantization parameter for theblock using the above-described approach. Next, based on the determinedweight, loop filter 120 determines a weight for the other blockaccording to a predetermined rule.

In addition, loop filter 120 may use a symmetrical filter when thequantization parameters for the two blocks are different or when thedifference between the quantization parameters for the two blocksexceeds a threshold value.

In addition, in FIG. 23, although weights are set using a linearfunction, but an arbitrary function other than the linear function or atable may be used. For example, a curve indicating the relationshipsbetween quantization parameters and quantization steps (quantizationwidths) may be used.

In addition, loop filter 120 may use a symmetrical filter without usingan asymmetrical filter when a quantization parameter exceeds a thresholdvalue. In addition, when a quantization parameter is described at adecimal accuracy, loop filter 120 may perform a calculation that is, forexample, a round-off, a round-up, a cut-off, or the like onto thequantization parameter and use the quantization parameter after beingsubjected to the calculation in the above-described processing.Alternatively, loop filter 120 may perform the processing taking intoaccount the decimal point level.

Although the plurality of approaches for determining errors have beendescribed in Embodiments 2 to 6, two or more of these approaches may becombined. In this case, loop filter 120 may perform weighting oncombined two or more elements.

Hereinafter, a variation is described.

Examples other than the examples of coding parameters described abovemay be used. For example, coding parameters may be the kind oforthogonal transform (such as Wavelet, DFT, lapped transform, or thelike), a block size (the width and height of a block), a motion vectordirection, the length of a motion vector, the number of referencepictures which are used in inter prediction, and information indicatinga reference filter characteristic. Alternatively, these parameters maybe used in combination. For example, loop filter 120 may use anasymmetrical filter only when the length of a block boundary correspondsto 16 pixels or less and a current pixel to be filtered is close to areference pixel in intra prediction, and may use a symmetrical filter inthe other cases. As another example, asymmetrical processing may beperformed only when a filter of a predetermined type among a pluralityof filter candidates has been used. For example, an asymmetricalprocessing may be used only when a variation by a reference filter iscalculated according to (A×(q1−p1)−B×(q2−p2)+C)/D. Here, A, B, C, and Dare constants. For example, A=9, B=3, C=8, and D=16 are satisfied. Inaddition, p1, p2, q1, and q2 are pixel values of pixels located across ablock boundary and are in a positional relationship indicated in FIG.12.

In addition, loop filter 120 may perform the processing on only one of aluminance signal and a chrominance signal or on the both. In addition,loop filter 120 may perform common processing or different processing onthe luminance signal and the chrominance signal. For example, loopfilter 120 may use different weights for the luminance signal and thechrominance signal, or may determine weights according to differentrules.

In addition, various kinds of parameters for use in the above processingmay be determined by encoder 100, or may be preset fixed values.

In addition, whether to perform the above processing or the details ofthe processing may be switched based on a predetermined unit. Examplesof the predetermined unit include a slice unit, a tile unit, a wavefrontdividing unit, or a CTU unit. In addition, the details of the processingare which one of the plurality of approaches described above is used, orparameters indicating weights, etc., or parameters for determiningthese.

In addition, loop filter 120 may limit the area in which the aboveprocessing are performed to a CTU boundary, a slice boundary, or a tileboundary.

In addition, the number of filter taps may vary between a symmetricalfilter and an asymmetrical filter.

In addition, loop filter 120 may change whether to perform the aboveprocessing or the details of the processing according to a frame type(I-frame, P-frame, or B-frame).

In addition, loop filter 120 may determine whether to perform theprocessing or the details of the processing according to whetherparticular processing at a pre-stage or a post-stage has been performed.

In addition, loop filter 120 may perform different processing accordingto the kind of the prediction mode used for a block, or may perform theabove processing only on a block for which a particular prediction modeis used. For example, loop filter 120 may perform different processingbetween a block for which intra prediction is used, a block for whichinter prediction is used, and a merged block.

In addition, encoder 100 may encode filter information which isparameters indicating whether to perform the above processing or thedetails of the processing. In other words, encoder 100 may generate anencoded bitstream including filter information. This filter informationmay include information indicating whether to perform the aboveprocessing on a luminance signal, information indicating whether toperform the above processing on a chrominance signal, informationindicating whether to change processing according to respectiveprediction modes, or other information.

In addition, decoder 200 may perform the above processing based onfilter information included in an encoded bitstream. For example,decoder 200 may determine whether to perform the above processing or thedetails of the processing, based on the filter information.

This aspect may be implemented in combination with one or more of theother aspects according to the present disclosure. In addition, part ofthe processes in the flowcharts, part of the constituent elements of theapparatuses, and part of the syntax described in this aspect may beimplemented in combination with other aspects.

Embodiment 7

In each of the embodiments, each of the functional blocks can normallybe implemented as an MPU, memory, or the like. In addition, theprocessing performed by each functional block is normally implemented bya program executor such as a processor reading and executing software (aprogram) recorded on a recording medium such as a ROM. The software maybe distributed by download, or the like, or may be recorded on arecording medium such as a semiconductor memory and then be distributed.It is to be noted that each functional block can naturally beimplemented as hardware (an exclusive circuit).

In addition, the processing described in each embodiment may beimplemented by performing centralized processing using a singleapparatus (system), or by performing distributed processing using aplurality of apparatuses. In addition, one or more processors mayexecute the program. In other words, any one of centralized processingand distributed processing may be performed.

Aspects of the present disclosure are not limited to the above examples,various modifications are possible, and these modifications, etc. may beencompassed in aspects of the present disclosure.

Furthermore, here, application examples of a video encoding method(image encoding method) or a video decoding method (image decodingmethod) indicated in each of the embodiments and a system using theapplication examples are described. The system is characterized byincluding an image encoder which performs an image encoding method, animage decoder which performs an image decoding method, and an imageencoder and decoder which performs both an image encoding method and animage decoding method. The other constituent elements in the system canbe appropriately modified according to cases.

[Usage Examples]

FIG. 24 illustrates an overall configuration of content providing systemex100 for implementing a content distribution service. The area in whichthe communication service is provided is divided into cells of desiredsizes, and base stations ex106, ex107, ex108, ex109, and ex110, whichare fixed wireless stations, are located in respective cells.

In content providing system ex100, devices including computer ex111,gaming device ex112, camera ex113, home appliance ex114, and smartphoneex115 are connected to internet ex101 via internet service providerex102 or communications network ex104 and base stations ex106 throughex110. Content providing system ex100 may combine and connect anycombination of the above elements. The devices may be directly orindirectly connected together via a telephone network or near fieldcommunication rather than via base stations ex106 through ex110, whichare fixed wireless stations. Moreover, streaming server ex103 isconnected to devices including computer ex111, gaming device ex112,camera ex113, home appliance ex114, and smartphone ex115 via, forexample, internet ex101. Streaming server ex103 is also connected to,for example, a terminal in a hotspot in airplane ex117 via satelliteex116.

Note that instead of base stations ex106 through ex110, wireless accesspoints or hotspots may be used. Streaming server ex103 may be connectedto communications network ex104 directly instead of via internet ex101or internet service provider ex102, and may be connected to airplaneex117 directly instead of via satellite ex116.

Camera ex113 is a device capable of capturing still images and video,such as a digital camera. Smartphone ex115 is a smartphone device,cellular phone, or personal handyphone system (PHS) phone that canoperate under the mobile communications system standards of the typical2G, 3G, 3.9G, and 4G systems, as well as the next-generation 5G system.

Home appliance ex118 is, for example, a refrigerator or a deviceincluded in a home fuel cell cogeneration system.

In content providing system ex100, a terminal including an image and/orvideo capturing function is capable of, for example, live streaming byconnecting to streaming server ex103 via, for example, base stationex106. When live streaming, a terminal (e.g., computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, orairplane ex117) performs the encoding processing described in the aboveembodiments on still-image or video content captured by a user via theterminal, multiplexes video data obtained via the encoding and audiodata obtained by encoding audio corresponding to the video, andtransmits the obtained data to streaming server ex103. In other words,the terminal functions as the image encoder according to one aspect ofthe present disclosure.

Streaming server ex103 streams transmitted content data to clients thatrequest the stream. Client examples include computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, andterminals inside airplane ex117, which are capable of decoding theabove-described encoded data. Devices that receive the streamed datadecode and reproduce the received data. In other words, the devices eachfunction as the image decoder according to one aspect of the presentdisclosure.

[Decentralized Processing]

Streaming server ex103 may be realized as a plurality of servers orcomputers between which tasks such as the processing, recording, andstreaming of data are divided. For example, streaming server ex103 maybe realized as a content delivery network (CDN) that streams content viaa network connecting multiple edge servers located throughout the world.In a CDN, an edge server physically near the client is dynamicallyassigned to the client. Content is cached and streamed to the edgeserver to reduce load times. In the event of, for example, some kind ofan error or a change in connectivity due to, for example, a spike intraffic, it is possible to stream data stably at high speeds since it ispossible to avoid affected parts of the network by, for example,dividing the processing between a plurality of edge servers or switchingthe streaming duties to a different edge server, and continuingstreaming.

Decentralization is not limited to just the division of processing forstreaming; the encoding of the captured data may be divided between andperformed by the terminals, on the server side, or both. In one example,in typical encoding, the processing is performed in two loops. The firstloop is for detecting how complicated the image is on a frame-by-frameor scene-by-scene basis, or detecting the encoding load. The second loopis for processing that maintains image quality and improves encodingefficiency. For example, it is possible to reduce the processing load ofthe terminals and improve the quality and encoding efficiency of thecontent by having the terminals perform the first loop of the encodingand having the server side that received the content perform the secondloop of the encoding. In such a case, upon receipt of a decodingrequest, it is possible for the encoded data resulting from the firstloop performed by one terminal to be received and reproduced on anotherterminal in approximately real time. This makes it possible to realizesmooth, real-time streaming.

In another example, camera ex113 or the like extracts a feature amountfrom an image, compresses data related to the feature amount asmetadata, and transmits the compressed metadata to a server. Forexample, the server determines the significance of an object based onthe feature amount and changes the quantization accuracy accordingly toperform compression suitable for the meaning of the image. Featureamount data is particularly effective in improving the precision andefficiency of motion vector prediction during the second compressionpass performed by the server. Moreover, encoding that has a relativelylow processing load, such as variable length coding (VLC), may behandled by the terminal, and encoding that has a relatively highprocessing load, such as context-adaptive binary arithmetic coding(CABAC), may be handled by the server.

In yet another example, there are instances in which a plurality ofvideos of approximately the same scene are captured by a plurality ofterminals in, for example, a stadium, shopping mall, or factory. In sucha case, for example, the encoding may be decentralized by dividingprocessing tasks between the plurality of terminals that captured thevideos and, if necessary, other terminals that did not capture thevideos and the server, on a per-unit basis. The units may be, forexample, groups of pictures (GOP), pictures, or tiles resulting fromdividing a picture. This makes it possible to reduce load times andachieve streaming that is closer to real-time.

Moreover, since the videos are of approximately the same scene,management and/or instruction may be carried out by the server so thatthe videos captured by the terminals can be cross-referenced. Moreover,the server may receive encoded data from the terminals, change referencerelationship between items of data or correct or replace picturesthemselves, and then perform the encoding. This makes it possible togenerate a stream with increased quality and efficiency for theindividual items of data.

Moreover, the server may stream video data after performing transcodingto convert the encoding format of the video data. For example, theserver may convert the encoding format from MPEG to VP, and may convertH.264 to H.265.

In this way, encoding can be performed by a terminal or one or moreservers. Accordingly, although the device that performs the encoding isreferred to as a “server” or “terminal” in the following description,some or all of the processes performed by the server may be performed bythe terminal, and likewise some or all of the processes performed by theterminal may be performed by the server. This also applies to decodingprocesses.

[3D, Multi-Angle]

In recent years, usage of images or videos combined from images orvideos of different scenes concurrently captured or the same scenecaptured from different angles by a plurality of terminals such ascamera ex113 and/or smartphone ex115 has increased. Videos captured bythe terminals are combined based on, for example, theseparately-obtained relative positional relationship between theterminals, or regions in a video having matching feature points.

In addition to the encoding of two-dimensional moving pictures, theserver may encode a still image based on scene analysis of a movingpicture either automatically or at a point in time specified by theuser, and transmit the encoded still image to a reception terminal.Furthermore, when the server can obtain the relative positionalrelationship between the video capturing terminals, in addition totwo-dimensional moving pictures, the server can generatethree-dimensional geometry of a scene based on video of the same scenecaptured from different angles. Note that the server may separatelyencode three-dimensional data generated from, for example, a pointcloud, and may, based on a result of recognizing or tracking a person orobject using three-dimensional data, select or reconstruct and generatea video to be transmitted to a reception terminal from videos capturedby a plurality of terminals.

This allows the user to enjoy a scene by freely selecting videoscorresponding to the video capturing terminals, and allows the user toenjoy the content obtained by extracting, from three-dimensional datareconstructed from a plurality of images or videos, a video from aselected viewpoint. Furthermore, similar to with video, sound may berecorded from relatively different angles, and the server may multiplex,with the video, audio from a specific angle or space in accordance withthe video, and transmit the result.

In recent years, content that is a composite of the real world and avirtual world, such as virtual reality (VR) and augmented reality (AR)content, has also become popular. In the case of VR images, the servermay create images from the viewpoints of both the left and right eyesand perform encoding that tolerates reference between the two viewpointimages, such as multi-view coding (MVC), and, alternatively, may encodethe images as separate streams without referencing. When the images aredecoded as separate streams, the streams may be synchronized whenreproduced so as to recreate a virtual three-dimensional space inaccordance with the viewpoint of the user.

In the case of AR images, the server superimposes virtual objectinformation existing in a virtual space onto camera informationrepresenting a real-world space, based on a three-dimensional positionor movement from the perspective of the user. The decoder may obtain orstore virtual object information and three-dimensional data, generatetwo-dimensional images based on movement from the perspective of theuser, and then generate superimposed data by seamlessly connecting theimages. Alternatively, the decoder may transmit, to the server, motionfrom the perspective of the user in addition to a request for virtualobject information, and the server may generate superimposed data basedon three-dimensional data stored in the server in accordance with thereceived motion, and encode and stream the generated superimposed datato the decoder. Note that superimposed data includes, in addition to RGBvalues, an a value indicating transparency, and the server sets the avalue for sections other than the object generated fromthree-dimensional data to, for example, 0, and may perform the encodingwhile those sections are transparent. Alternatively, the server may setthe background to a predetermined RGB value, such as a chroma key, andgenerate data in which areas other than the object are set as thebackground.

Decoding of similarly streamed data may be performed by the client(i.e., the terminals), on the server side, or divided therebetween. Inone example, one terminal may transmit a reception request to a server,the requested content may be received and decoded by another terminal,and a decoded signal may be transmitted to a device having a display. Itis possible to reproduce high image quality data by decentralizingprocessing and appropriately selecting content regardless of theprocessing ability of the communications terminal itself. In yet anotherexample, while a TV, for example, is receiving image data that is largein size, a region of a picture, such as a tile obtained by dividing thepicture, may be decoded and displayed on a personal terminal orterminals of a viewer or viewers of the TV. This makes it possible forthe viewers to share a big-picture view as well as for each viewer tocheck his or her assigned area or inspect a region in further detail upclose.

In the future, both indoors and outdoors, in situations in which aplurality of wireless connections are possible over near, mid, and fardistances, it is expected to be able to seamlessly receive content evenwhen switching to data appropriate for the current connection, using astreaming system standard such as MPEG-DASH. With this, the user canswitch between data in real time while freely selecting a decoder ordisplay apparatus including not only his or her own terminal, but also,for example, displays disposed indoors or outdoors. Moreover, based on,for example, information on the position of the user, decoding can beperformed while switching which terminal handles decoding and whichterminal handles the displaying of content. This makes it possible to,while in route to a destination, display, on the wall of a nearbybuilding in which a device capable of displaying content is embedded oron part of the ground, map information while on the move. Moreover, itis also possible to switch the bit rate of the received data based onthe accessibility to the encoded data on a network, such as when encodeddata is cached on a server quickly accessible from the receptionterminal or when encoded data is copied to an edge server in a contentdelivery service.

[Scalable Encoding]

The switching of content will be described with reference to a scalablestream, illustrated in FIG. 25, that is compression coded viaimplementation of the moving picture encoding method described in theabove embodiments. The server may have a configuration in which contentis switched while making use of the temporal and/or spatial scalabilityof a stream, which is achieved by division into and encoding of layers,as illustrated in FIG. 25. Note that there may be a plurality ofindividual streams that are of the same content but different quality.In other words, by determining which layer to decode up to based oninternal factors, such as the processing ability on the decoder side,and external factors, such as communication bandwidth, the decoder sidecan freely switch between low resolution content and high resolutioncontent while decoding. For example, in a case in which the user wantsto continue watching, at home on a device such as a TV connected to theinternet, a video that he or she had been previously watching onsmartphone ex115 while on the move, the device can simply decode thesame stream up to a different layer, which reduces server side load.

Furthermore, in addition to the configuration described above in whichscalability is achieved as a result of the pictures being encoded perlayer and the enhancement layer is above the base layer, the enhancementlayer may include metadata based on, for example, statisticalinformation on the image, and the decoder side may generate high imagequality content by performing super-resolution imaging on a picture inthe base layer based on the metadata. Super-resolution imaging may beimproving the SN ratio while maintaining resolution and/or increasingresolution. Metadata includes information for identifying a linear or anon-linear filter coefficient used in super-resolution processing, orinformation identifying a parameter value in filter processing, machinelearning, or least squares method used in super-resolution processing.

Alternatively, a configuration in which a picture is divided into, forexample, tiles in accordance with the meaning of, for example, an objectin the image, and on the decoder side, only a partial region is decodedby selecting a tile to decode, is also acceptable. Moreover, by storingan attribute about the object (person, car, ball, etc.) and a positionof the object in the video (coordinates in identical images) asmetadata, the decoder side can identify the position of a desired objectbased on the metadata and determine which tile or tiles include thatobject. For example, as illustrated in FIG. 26, metadata is stored usinga data storage structure different from pixel data such as an SEImessage in HEVC. This metadata indicates, for example, the position,size, or color of the main object.

Moreover, metadata may be stored in units of a plurality of pictures,such as stream, sequence, or random access units. With this, the decoderside can obtain, for example, the time at which a specific personappears in the video, and by fitting that with picture unit information,can identify a picture in which the object is present and the positionof the object in the picture.

[Web Page Optimization]

FIG. 27 illustrates an example of a display screen of a web page on, forexample, computer ex111. FIG. 28 illustrates an example of a displayscreen of a web page on, for example, smartphone ex115. As illustratedin FIG. 27 and FIG. 28, a web page may include a plurality of imagelinks which are links to image content, and the appearance of the webpage differs depending on the device used to view the web page. When aplurality of image links are viewable on the screen, until the userexplicitly selects an image link, or until the image link is in theapproximate center of the screen or the entire image link fits in thescreen, the display apparatus (decoder) displays, as the image links,still images included in the content or I pictures, displays video suchas an animated gif using a plurality of still images or I pictures, forexample, or receives only the base layer and decodes and displays thevideo.

When an image link is selected by the user, the display apparatusdecodes giving the highest priority to the base layer. Note that ifthere is information in the HTML code of the web page indicating thatthe content is scalable, the display apparatus may decode up to theenhancement layer. Moreover, in order to guarantee real timereproduction, before a selection is made or when the bandwidth isseverely limited, the display apparatus can reduce delay between thepoint in time at which the leading picture is decoded and the point intime at which the decoded picture is displayed (that is, the delaybetween the start of the decoding of the content to the displaying ofthe content) by decoding and displaying only forward reference pictures(I picture, P picture, forward reference B picture). Moreover, thedisplay apparatus may purposely ignore the reference relationshipbetween pictures and coarsely decode all B and P pictures as forwardreference pictures, and then perform normal decoding as the number ofpictures received over time increases.

[Autonomous Driving]

When transmitting and receiving still image or video data such two- orthree-dimensional map information for autonomous driving or assisteddriving of an automobile, the reception terminal may receive, inaddition to image data belonging to one or more layers, information on,for example, the weather or road construction as metadata, and associatethe metadata with the image data upon decoding. Note that metadata maybe assigned per layer and, alternatively, may simply be multiplexed withthe image data.

In such a case, since the automobile, drone, airplane, etc., includingthe reception terminal is mobile, the reception terminal can seamlesslyreceive and decode while switching between base stations among basestations ex106 through ex110 by transmitting information indicating theposition of the reception terminal upon reception request. Moreover, inaccordance with the selection made by the user, the situation of theuser, or the bandwidth of the connection, the reception terminal candynamically select to what extent the metadata is received or to whatextent the map information, for example, is updated.

With this, in content providing system ex100, the client can receive,decode, and reproduce, in real time, encoded information transmitted bythe user.

[Streaming of Individual Content]

In content providing system ex100, in addition to high image quality,long content distributed by a video distribution entity, unicast ormulticast streaming of low image quality, short content from anindividual is also possible. Moreover, such content from individuals islikely to further increase in popularity. The server may first performediting processing on the content before the encoding processing inorder to refine the individual content. This may be achieved with, forexample, the following configuration.

In real-time while capturing video or image content or after the contenthas been captured and accumulated, the server performs recognitionprocessing based on the raw or encoded data, such as capture errorprocessing, scene search processing, meaning analysis, and/or objectdetection processing. Then, based on the result of the recognitionprocessing, the server—either when prompted or automatically—edits thecontent, examples of which include: correction such as focus and/ormotion blur correction; removing low-priority scenes such as scenes thatare low in brightness compared to other pictures or out of focus; objectedge adjustment; and color tone adjustment. The server encodes theedited data based on the result of the editing. It is known thatexcessively long videos tend to receive fewer views. Accordingly, inorder to keep the content within a specific length that scales with thelength of the original video, the server may, in addition to thelow-priority scenes described above, automatically clip out scenes withlow movement based on an image processing result. Alternatively, theserver may generate and encode a video digest based on a result of ananalysis of the meaning of a scene.

Note that there are instances in which individual content may includecontent that infringes a copyright, moral right, portrait rights, etc.Such an instance may lead to an unfavorable situation for the creator,such as when content is shared beyond the scope intended by the creator.Accordingly, before encoding, the server may, for example, edit imagesso as to blur faces of people in the periphery of the screen or blur theinside of a house, for example. Moreover, the server may be configuredto recognize the faces of people other than a registered person inimages to be encoded, and when such faces appear in an image, forexample, apply a mosaic filter to the face of the person. Alternatively,as pre- or post-processing for encoding, the user may specify, forcopyright reasons, a region of an image including a person or a regionof the background be processed, and the server may process the specifiedregion by, for example, replacing the region with a different image orblurring the region. If the region includes a person, the person may betracked in the moving picture the head region may be replaced withanother image as the person moves.

Moreover, since there is a demand for real-time viewing of contentproduced by individuals, which tends to be small in data size, thedecoder first receives the base layer as the highest priority andperforms decoding and reproduction, although this may differ dependingon bandwidth. When the content is reproduced two or more times, such aswhen the decoder receives the enhancement layer during decoding andreproduction of the base layer and loops the reproduction, the decodermay reproduce a high image quality video including the enhancementlayer. If the stream is encoded using such scalable encoding, the videomay be low quality when in an unselected state or at the start of thevideo, but it can offer an experience in which the image quality of thestream progressively increases in an intelligent manner. This is notlimited to just scalable encoding; the same experience can be offered byconfiguring a single stream from a low quality stream reproduced for thefirst time and a second stream encoded using the first stream as areference.

[Other Usage Examples]

The encoding and decoding may be performed by LSI ex500, which istypically included in each terminal. LSI ex500 may be configured of asingle chip or a plurality of chips. Software for encoding and decodingmoving pictures may be integrated into some type of a recording medium(such as a CD-ROM, a flexible disk, or a hard disk) that is readable by,for example, computer ex111, and the encoding and decoding may beperformed using the software. Furthermore, when smartphone ex115 isequipped with a camera, the video data obtained by the camera may betransmitted. In this case, the video data is coded by LSI ex500 includedin smartphone ex115.

Note that LSI ex500 may be configured to download and activate anapplication. In such a case, the terminal first determines whether it iscompatible with the scheme used to encode the content or whether it iscapable of executing a specific service. When the terminal is notcompatible with the encoding scheme of the content or when the terminalis not capable of executing a specific service, the terminal firstdownloads a codec or application software then obtains and reproducesthe content.

Aside from the example of content providing system ex100 that usesinternet ex101, at least the moving picture encoder (image encoder) orthe moving picture decoder (image decoder) described in the aboveembodiments may be implemented in a digital broadcasting system. Thesame encoding processing and decoding processing may be applied totransmit and receive broadcast radio waves superimposed with multiplexedaudio and video data using, for example, a satellite, even though thisis geared toward multicast whereas unicast is easier with contentproviding system ex100.

[Hardware Configuration]

FIG. 29 illustrates smartphone ex115. FIG. 30 illustrates aconfiguration example of smartphone ex115. Smartphone ex115 includesantenna ex450 for transmitting and receiving radio waves to and frombase station ex110, camera ex465 capable of capturing video and stillimages, and display ex458 that displays decoded data, such as videocaptured by camera ex465 and video received by antenna ex450. Smartphoneex115 further includes user interface ex466 such as a touch panel, audiooutput unit ex457 such as a speaker for outputting speech or otheraudio, audio input unit ex456 such as a microphone for audio input,memory ex467 capable of storing decoded data such as captured video orstill images, recorded audio, received video or still images, and mail,as well as decoded data, and slot ex464 which is an interface for SIMex468 for authorizing access to a network and various data. Note thatexternal memory may be used instead of memory ex467.

Moreover, main controller ex460 which comprehensively controls displayex458 and user interface ex466, power supply circuit ex461, userinterface input controller ex462, video signal processor ex455, camerainterface ex463, display controller ex459, modulator/demodulator ex452,multiplexer/demultiplexer ex453, audio signal processor ex454, slotex464, and memory ex467 are connected via bus ex470.

When the user turns the power button of power supply circuit ex461 on,smartphone ex115 is powered on into an operable state by each componentbeing supplied with power from a battery pack.

Smartphone ex115 performs processing for, for example, calling and datatransmission, based on control performed by main controller ex460, whichincludes a CPU, ROM, and RAM. When making calls, an audio signalrecorded by audio input unit ex456 is converted into a digital audiosignal by audio signal processor ex454, and this is applied with spreadspectrum processing by modulator/demodulator ex452 and digital-analogconversion and frequency conversion processing by transmitter/receiverex451, and then transmitted via antenna ex450. The received data isamplified, frequency converted, and analog-digital converted, inversespread spectrum processed by modulator/demodulator ex452, converted intoan analog audio signal by audio signal processor ex454, and then outputfrom audio output unit ex457. In data transmission mode, text,still-image, or video data is transmitted by main controller ex460 viauser interface input controller ex462 as a result of operation of, forexample, user interface ex466 of the main body, and similar transmissionand reception processing is performed. In data transmission mode, whensending a video, still image, or video and audio, video signal processorex455 compression encodes, via the moving picture encoding methoddescribed in the above embodiments, a video signal stored in memoryex467 or a video signal input from camera ex465, and transmits theencoded video data to multiplexer/demultiplexer ex453. Moreover, audiosignal processor ex454 encodes an audio signal recorded by audio inputunit ex456 while camera ex465 is capturing, for example, a video orstill image, and transmits the encoded audio data tomultiplexer/demultiplexer ex453. Multiplexer/demultiplexer ex453multiplexes the encoded video data and encoded audio data using apredetermined scheme, modulates and converts the data usingmodulator/demodulator (modulator/demodulator circuit) ex452 andtransmitter/receiver ex451, and transmits the result via antenna ex450.

When video appended in an email or a chat, or a video linked from a webpage, for example, is received, in order to decode the multiplexed datareceived via antenna ex450, multiplexer/demultiplexer ex453demultiplexes the multiplexed data to divide the multiplexed data into abitstream of video data and a bitstream of audio data, supplies theencoded video data to video signal processor ex455 via synchronous busex470, and supplies the encoded audio data to audio signal processorex454 via synchronous bus ex470. Video signal processor ex455 decodesthe video signal using a moving picture decoding method corresponding tothe moving picture encoding method described in the above embodiments,and video or a still image included in the linked moving picture file isdisplayed on display ex458 via display controller ex459. Moreover, audiosignal processor ex454 decodes the audio signal and outputs audio fromaudio output unit ex457. Note that since real-time streaming is becomingmore and more popular, there are instances in which reproduction of theaudio may be socially inappropriate depending on the user's environment.Accordingly, as an initial value, a configuration in which only videodata is reproduced, i.e., the audio signal is not reproduced, ispreferable. Audio may be synchronized and reproduced only when an input,such as when the user clicks video data, is received.

Although smartphone ex115 was used in the above example, threeimplementations are conceivable: a transceiver terminal including bothan encoder and a decoder; a transmitter terminal including only anencoder; and a receiver terminal including only a decoder. Further, inthe description of the digital broadcasting system, an example is givenin which multiplexed data obtained as a result of video data beingmultiplexed with, for example, audio data, is received or transmitted,but the multiplexed data may be video data multiplexed with data otherthan audio data, such as text data related to the video. Moreover, thevideo data itself rather than multiplexed data maybe received ortransmitted.

Although main controller ex460 including a CPU is described ascontrolling the encoding or decoding processes, terminals often includeGPUs. Accordingly, a configuration is acceptable in which a large areais processed at once by making use of the performance ability of the GPUvia memory shared by the CPU and GPU or memory including an address thatis managed so as to allow common usage by the CPU and GPU. This makes itpossible to shorten encoding time, maintain the real-time nature of thestream, and reduce delay. In particular, processing relating to motionestimation, deblocking filtering, sample adaptive offset (SAO), andtransformation/quantization can be effectively carried out by the GPUinstead of the CPU in units of, for example pictures, all at once.

This aspect may be implemented in combination with one or more of theother aspects according to the present disclosure. In addition, part ofthe processes in the flowcharts, part of the constituent elements of theapparatuses, and part of the syntax described in this aspect may beimplemented in combination with other aspects.

Although only some exemplary embodiments of the present disclosure havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the present disclosure. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to encoders, decoders, encodingmethods, and decoding methods.

What is claimed is:
 1. A decoder comprising: processing circuitry; and amemory coupled to the processing circuitry, wherein the processingcircuitry is configured to: select a first filter for a first blockbased at least on a block size of the first block, the first filterincluding a first set of filter coefficients and a first set of offsets;select a second filter for a second block based at least on a block sizeof the second block, the second filter including a second set of filtercoefficients and a second set of offsets; and change values of pixels inthe first block and the second block to filter a boundary between thefirst block and the second block, by performing multiplication with eachcoefficient in the first set of filter coefficients as a multiplier, byperforming multiplication with each coefficient in the second set offilter coefficients as a multiplier, and by using the first set ofoffsets and the second set of offsets, the pixels in the first block andthe second block being arranged along a straight line across theboundary, wherein the first set of filter coefficients applied in thefirst block and the second set of filter coefficients applied in thesecond block are selected to be asymmetrical with respect to theboundary based on the block sizes of the first block and the secondblock, and wherein the first set of offsets and the second set ofoffsets are symmetric with respect to the boundary.
 2. A decodercomprising: processing circuitry; and a memory coupled to the processingcircuitry, wherein the processing circuitry is configured to: selectfilter coefficients based on block sizes of a first block and a secondblock in an image, the filter coefficients including a first set offilter coefficients and a first set of offsets for the first block, anda second set of filter coefficients and a second set of offsets for thesecond block; and change values of pixels in the first block and thesecond block, by performing multiplication with each coefficient in thefirst set of filter coefficients as a multiplier, by performingmultiplication with each coefficient in the second set of filtercoefficients as a multiplier, and by using the first set of offsets andthe second set of offsets, the pixels in the first block and the secondblock being arranged along a straight line across a boundary between thefirst block and the second block, wherein the first set of filtercoefficients applied in the first block and the second set of filtercoefficients applied in the second block are selected to be asymmetricalwith respect to the boundary based on the block sizes of the first blockand the second block, and wherein the first set of offsets and thesecond set of offsets are symmetric with respect to the boundary.